Working of Night Vision Technology

How Night Vision Works

Gyro-stabilized day/night binoculars manufactured by B.E. Meyers Company.

­ The first thing you probably think of when you see the words night vision is a spy or action movie you've seen, in which someone straps on a pair of night-vision goggles to find someone else in a dark building on a moonless night. And you may have wondered "Do those things really work? Can you actually see in the dark?"


The answer is most definitely yes. With the proper night-vision equipment, you can see a person standing over 200 yards (183 m) away on a moonless, cloudy night! Night vision can work in two very different ways, depending on the technology used.

• Image enhancement - This works by collecting the tiny amounts of light, including the lower portion of the infrared light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that we can easily observe the image.
• Thermal imaging - This technology operates by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this light than cooler objects like trees or buildings.

Here, you will learn about the two major night-vision technologies. We'll also discuss the various types of night-vision equipment and applications. But first, let's talk about infrared light.

Working of RFID

How RFID Works

An RFID tag.

Long checkout lines at the grocery store are one of the biggest complaints about the shopping experience. Soon, these lines could disappear when the ubiquitous Universal Product Code (UPC) bar code is replaced by smart labels, also called radio frequency identification (RFID) tags. RFID tags are intelligent bar codes that can talk to a networked system to track every product that you put in your shopping cart.
Imagine going to the grocery store, filling up your cart and walking right out the door. No longer will you have to wait as someone rings up each item in your cart one at a time. Instead, these RFID tags will communicate with an electronic reader that will detect every item in the cart and ring each up almost instantly. The reader will be connected to a large network that will send information on your products to the retailer and product manufacturers. Your bank will then be notified and the amount of the bill will be deducted from your account. No lines, no waiting.

RFID tags, a technology once limited to tracking cattle, are tracking consumer products worldwide. Many manufacturers use the tags to track the location of each product they make from the time it's made until it's pulled off the shelf and tossed in a shopping cart.
Outside the realm of retail merchandise, RFID tags are tracking vehicles, airline passengers, Alzheimer's patients and pets. Soon, they may even track your preference for chunky or creamy peanut butter. Some critics say RFID technology is becoming too much a part of our lives -- that is, if we're even aware of all the parts of our lives that it affects.
In this article, you'll learn about the types of RFID tags and how these tags can be tracked through the entire supply chain. We'll also look at the non-commercial uses of RFID tags and how the Departments of State and Homeland Security are using them. Lastly, we'll examine what some critics consider an Orwellian application of RFID tags in animals, humans and our society.

Reinventing the Bar Code

Barcodes, like this one found on a soda can, are found on almost everything we buy.

­Almost everything that you buy from retailers has a UPC bar code printed on it. These bar codes help manufacturers and retailers keep track of inventory. They also give valuable ­information about the quantity of products being bought and, to some extent, by whom the products are being bought. These codes serve as product fingerprints made of machine-readable parallel bars that store binary code.
Created in the early 1970s to speed up the check out process, bar codes have a few disadvantages:

• In order to keep up with inventories, companies must scan each bar code on every box of a particular product.
• Going through the checkout line involves the same process of scanning each bar code on each item.
• Bar code is a read-only technology, meaning that it cannot send out any information.

RFID tags are an improvement over bar codes because the tags have read and write capabilities. Data stored on RFID tags can be changed, updated and locked. Some stores that have begun using RFID tags have found that the technology offers a better way to track merchandise for stocking and marketing purposes. Through RFID tags, stores can see how quickly the products leave the shelves and who's buying them.

In addition to retail merchandise, RFID tags have also been added to transportation devices like highway toll passcards and subway passes. Because of their ability to store data so efficiently, RFID tags can tabulate the cost of tolls and fares and deduct the cost electronically from the amount of money that the user places on the card. Rather than waiting to pay a toll at a tollbooth or shelling out coins at a token counter, passengers use RFID chip-embedded passes like debit cards.

But would you entrust your medical history to an RFID tag? How about your home address or your baby's safety? Let's look at two types of RFID tags and how they store and transmit data before we move past grocery store purchase­s to human lives.
­

Bar Code HistoryAt 8:01 a.m. on June 26, 1974, a customer at Marsh's supermarket in Troy, OH, made the first purchase of a product with a barcode, a 10-pack of Wrigley's Juicy Fruit Gum. This began a new era in retail that sped up checkout lines and gave companies a more efficient method for inventory control. That pack of gum took its place in American history and is currently on display at the Smithsonian Institution's National Museum of American History. That historical purchase was the culmination of nearly 30 years of research and development. The first system for automatic product coding was patented by Bernard Silver and Norman Woodland, both graduate students at the Drexel Institute of Technology (now Drexel University). They used a pattern of ink that glowed under ultraviolet light. This system was too expensive and the ink wasn't very stable. The system we use today was unveiled by IBM in 1973 and uses readers designed by NCR.

 

RFID Tags Past and Present

RFID technology has been around since 1970, but until recently, it has been too expensive to use on a large scale. Originally, RFID tags were used to track large items, like cows, railroad cars and airline luggage, that were shipped over long distances, These original tags, called inductively coupled RFID tags, were complex systems of metal coils, antennae and glass.
Inductively coupled RFID tags were powered by a magnetic field generated by the RFID reader. Electrical current has an electrical component and a magnetic component -- it is electromagnetic. Because of this, you can create a magnetic field with electricity, and you can create electrical current with a magnetic field. The name "inductively coupled" comes from this process -- the magnetic field inducts a current in the wire. You can learn more in How Electromagnets Work.

This RFID tag from Texas Instruments dates back to 1999, when it was used to track luggage.

Capacitively coupled tags were created next in an attempt to lower the technology's cost. These were meant to be disposable tags that could be applied to less expensive merchandise and made as universal as bar codes. Capacitively coupled tags used conductive carbon ink instead of metal coils to transmit data. The ink was printed on paper labels and scanned by readers. Motorola's BiStatix RFID tags were the frontrunners in this technology. They used a silicon chip that was only 3mm wide and stored 96 bits of information. This technology didn't catch on with retailers, and BiStatix was shut down in 2001 [source: RFID Journal].

Newer innovations in the RFID industry include active, semi-active, and passive RFID tags. These tags can store up to 2 kilobytes of data and are composed of a microchip, antenna, and, in the case of active and semi-passive tags, a battery. The tag's components are enclosed within plastic, silicon or sometimes glass.
At a basic level, each tag works in the same way:

• Data­ stored within an RFID tag's microchip waits to be read.
• The tag's antenna receives electromagnetic energy from an RFID reader's antenna.
• Using power from its internal battery or power harvested from the reader's electromagnetic field, the tag sends radio waves back to the reader.
• ­The reader picks up the tag's radio waves and interprets the frequencies as meaningful data.

Inductively coupled and capacitively coupled RFID tags aren't used as commonly today because they are expensive and bulky. In the next section, we'll learn more about active, semi-passive and passive RFID tags.

Active, Semi-passive and Passive RFID Tags

Active, semi-passive and passive RFID tags are making RFID technology more accessible and prominent in our world. These tags are less expensive to produce, and they can be made small enough to fit on almost any product.
Active and semi-passive RFID tags use internal batteries to power their circuits. An active tag also uses its battery to broadcast radio waves to a reader, whereas a semi-passive tag relies on the reader to supply its power for broadcasting. Because these tags contain more hardware than passive RFID tags, they are more expensive. Active and semi-passive tags are reserved for costly items that are read over greater distances -- they broadcast high frequencies from 850 to 950 MHz that can be read 100 feet or more away. If it is necessary to read the tags from even farther away, additional batteries can boost a tag's range to over 300 feet (100 meters) [source: RFID Journal].
Passive RFID tags rely entirely on the reader as their power source. These tags are read up to 20 feet away, and they have lower production costs, meaning that they can be applied to less expensive merchandise. These tags are manufactured to be disposable, along with the disposable consumer goods on which they are placed. Whereas a railway car would have an active RFID tag, a bottle of shampoo would have a passive tag.
Another factor that influences the cost of RFID tags is data storage. There are three storage types: read-write, read-only and WORM (write once, read many). A read-write tag's data can be added to or overwritten. Read-only tags cannot be added to or overwritten -- they contain only the data that is stored in them when they were made. WORM tags can have additional data (like another serial number) added once, but they cannot be overwritten.

This tiny RFID tag will be placed on a bottle of moisturizer.

Most pass­ive RFID tags cost between 7 and 20 cents each [source: RFID Journal]. Active and semi-passive tags are more expensive, and RFID manufacturers typically do not quote prices for these tags without first determining their range, ­storage type and quantity. The RFID industry's goal is to get the cost of a passive RFID tag down to 5 cents each once more merchandisers adopt it.

In the next section, we'll learn how this technology could be used to create a global system of RFID tags that link to the Internet. ­

 

Talking Tags

When the RFID industry is able to lower the price of tags, it will lead to a ubiquitous network of smart packages that track every phase of the supply chain. Store ­shelves will be full of smart-labeled products that can be tracked from purchase to trash can. The shelves themselves will communicate wirelessly with the network. The tags will be just one component of this large product-tracking network.
The other two pieces to this network will be the readers that communicate with the tags and the Internet, which will provide communications lines for the network. Let's look at a real-world scenario of this system:

• At the grocery store, you buy a carton of milk. The milk containers will have an RFID tag that stores the milk's expiration date and price. When you lift the milk from the shelf, the shelf may display the milk's specific expiration date, or the information could be wirelessly sent to your personal digital assistant or cell phone.
• As you exit the store, you pass through doors with an embedded tag reader. This reader tabulates the cost of all the items in your shopping cart and sends the grocery bill to your bank, which deducts the amount from your account. Product manufacturers know that you've bought their product, and the store's computers know exactly how many of each product need to be reordered.
• Once you get home, you put your milk in the refrigerator, which is also equipped with a tag reader. This smart refrigerator is capable of tracking all of the groceries stored in it. It can track the foods you use, how often you restock your refrigerator and can let you know when that milk and other foods spoil.
• Products are also tracked when they are thrown into a trash can or recycle bin. At this point, your refrigerator could add milk to your grocery list, or you could program the fridge to order these items automatically.
• Based on the products you buy, your grocery store gets to know your unique preferences. Instead of receiving generic newsletters with weekly grocery specials, you might receive one created just for you. If you have two school-age children and a puppy, your grocery store can use customer-specific marketing by sending you coupons for items like juice boxes and dog food.

In order for this system to work, each product will be given a unique product number. MIT's Auto-ID Center is working on an Electronic Product Code (EPC) identifier that could replace the UPC. Every smart label could contain 96 bits of information, including the product manufacturer, product name and a 40-bit serial number. Using this system, a smart label would communicate with a network called the Object Naming Service. This database would retrieve information about a product and then direct information to the manufacturer's computers.
The information stored on the smart labels would be written in a Product Markup Language (PML), which is based on the eXtensible Markup Language (XML). PML would allow all computers to communicate with any computer system similar to the way that Web servers read Hyper Text Markup Language (HTML), the common language used to create Web pages.
We're not at this point yet, but RFID tags are more prominent in your life than you may realize. Wal-Mart and Best Buy are just two major merchandisers that use RFID tags for stocking and marketing purposes.
Some critics find the idea of merchandisers tracking and recording purchases to be alarming. But retail isn't the only industry using RFID technology. In the next section, we'll learn how the government is putting RFID tags to use.­

Government-issued RFIDs

REAL ID From air traffic to road traffic, security is becoming a more pressing issue, and some people feel that they're being monitored more closely than ever before. REAL ID, a program developed by the 9/11 Commission, is intended to improve the way that official identification is issued. While the REAL ID has yet to be approved (and is being heatedly debated), the first proposed REAL ID is the REAL ID driver's license. DHS issued a Notice of Proposed Rulemaking for the REAL ID driver's license on March 1, 2007. The REAL ID driver's license can be enhanced to give you easy border-crossing access to Canada, and beyond a standard driver's license, it also grants you access to federal facilities, federal aircraft and nuclear power plants [source: Department of Homeland Security]. States will choose whether or not to embed RFID chips in the REAL ID driver's license in place of the current 2-D bar code.

While many consumers happily -- or obliviously -- buy merchandise tracked with RFID tags, some people are up in arms about the federal government's legislation mandating that passports be embedded with RFID microchips.

On Aug. 14, 2006, the Department of State began issuing electronic passports, or e-passports. Prompted by the terrorist attacks of Sept.11, 2001 the Department of Homeland Security (DHS) proposed the e-passport as a security measure for air travel safety, border security and more efficient customs procedures at airports. The e-passport's enhanced security features -- a chip identification number, digital signature and photograph that acts as a biometric identifier -- make the passport impossible to forge.
The e-passport will help improve security, but with so much personal information embedded in the document, there have been many concerns raised about the e-passport's potential for identity theft. Two possible forms of identity theft that could occur with e-passports are:

• Skimming happens when someone uses an RFID reader to scan data from an RFID chip without the e-passport holder's knowledge.
• Eavesdropping happens when someone reads the frequencies emitted from the RFID chip as it is scanned by an official reader.

However, the DHS insists that the e-passport is perfectly safe to use and that proper precautions have been taken to ensure user confidentiality.

• For protection against skimming, the e-passport contains a metallic anti-skimming device. This device is a radio shield inserted between the passport's cover and first page. When the e-passport is closed, it can't be scanned at all; when it's open, it can only be read by a scanner that is less than 10 centimeters away [source: Department of State].
• To guard against eavesdropping, DHS has mandated that all areas where the e-passport is scanned be thoroughly covered and enclosed so that signals cannot be picked up beyond the authorized RFID reader.

The Australian passport served as a model for the new United States e-passport.

­The e-passport costs $97. While the cost to you may seem steep, the cost of installing RFID readers in airports is even more staggering. Adopting the e-passport will require gradual change, but aut­horities are already discussing what added security features and improved biometrics the next series of e-passports will have.
The debate over e-passports pales in comparison to debates over human chipping. Next, we'll learn what RFID microchips are doing in livi­ng things.
­

 

Animal and Human Chipping

Animal chipping is nothing new -- farmers have been tracking livestock for years using RFID technology. But companies are turning animal chipping for pets into big business, and some companies are offering options for human chipping.

I Want You. . .To Chip Your Pets On Sept. 26, 2006, the Secretary of the Navy mandated that all Navy and Marine Corps pet owners have their pets implanted with RFID chips [source: Secretary of the Navy]. This order came partly as a result of pet abandonment when some military families relocate and leave their pets behind.

RFID pet recovery systems rely on tiny microchips the size of a grain of rice that contains the pet owner's contact information and sometimes an animal's medical history. Veterinarians scan lost pets with an RFID reader to determine whether or not the pet has a microchip. But the system can break down here. There are many competing pet recovery systems and consequently, many pet microchips. The Humane Society of the United States has been campaigning for development of a universal RFID reader that vets could use to read a pet's microchip, no matter its manufacturer or year of manufacture. In November 2005, President George Bush signed a bill for the standardization of pet microchips and a national database of pet owner information [source: RFID Journal].
Even though the FDA approved the implantation of RFID microchips in animals and humans in 2004, research from as far back as 1996 shows that these implants can cause cancerous tumors in lab rats and mice [source: Washington Post]. Specifically, the implants caused sarcomas, which affect body tissue. No studies have proven yet that cancer can form in animals other than lab rats and mice, and it's still too early to tell what effects the chips can have on humans. Despite this evidence, or lack thereof, other disadvantages of human chipping may outweigh its advantages.
VeriChip Corp. is leading the human chipping business. The company makes microchips with unique identification numbers that link to a VeriChip medical database. The VeriChip database contains emergency contact information and medical histories. Patients with serious medical issues and Alzheimer's are ideal candidates for the VeriChip. In addition to a one-time implantation fee, VeriChip charges annual fees based on how much information you want in the database -- you can choose to have just your name and contact information or your full medical history. VeriChip is still growing, so there are not RFID readers in every hospital. Also, doctors might not scan every patient to check for a chip, so depending on the hospital or doctor, your VeriChip could prove useless.­

The Jacobs family of Boca Raton, FL served as early subjects for VeriChip implants. In 2002, Jeffrey, Leslie and their son Derek were chipped.

­­One VeriChip with greater rates of success is the Hugs Infant Protection Program. Under this RFID monitoring system, newborns in some hospital nurseries wear ankle bracelets with RFID chips. If an unauthorized person tries to remove a baby from the hospital, an alarm is sounded at the nurses' station and at exit doors. You can read more about successful infant abduction prevention on the VeriChip Web site.
 we'll hear what RFID critics have to say about tracking devices in our modern world.
­

RFID and SIDS

One researcher has developed an RFID system that monitors a baby's carbon dioxide levels in order to prevent Sudden Infant Death Syndrome (SIDS). Under this system, sensors attached to a crib sound an alert if they detect that the baby has stopped breathing, potentially saving young lives. Read more about this SIDS prevention system in the RFID Journal.­

RFID Criticism

George Orwell's "1984" "1984" tells the story of a society in which all citizens are patrolled by the Thought Police, who ensure that no one has any independent or rebellious thoughts that aren't sanctioned by the Party. In this society, everyone answers to Big Brother -- the ultimate authority on education, government and recreation. When critics of RFID call the technology "Orwellian," they mean that the technology is too invasive and that businesses and government are made too knowledgeable of our private actions, just like Big Brother watching us.

As with many new technologies, people fear what they don't understand. In the case of RFID, consumers have many fears, some of which may be justified. This debate may be one of the few in which you'll find the American Civil Liberties Union and Christian Coalition on the same side.
Human chipping has seemingly higher stakes than merchandise tagging, and RFID critics are concerned that human chipping may one day become mandatory. When the company CityWatcher.com chipped two of its employees in 2006, these fears spun out of control. CityWatcher.com insisted that the employees were not forced to be chipped -- they volunteered for the microchip implants for easier access to secured vaults where confidential documents are stored. Other employees declined the implants, and their positions with the company were unaffected.

Mandatory Human Chipping In October 2007, California governor Arnold Schwarzenegger signed a bill making it unlawful for any employer to force an employee to be chipped. California is also working to ban RFID chips in REAL ID drivers' licenses [source: RFID Journal].

­Aside from the limitations of VeriChip scanning discussed in the last section, human chipping has profound religious and civil liberty implications for some people. Some believe that human chipping is foretelling a biblical prophecy from the Book of Revelation, interpreting the chip as the "Mark of the Beast." To others concerned with civil liberties, the chip is bringing us one step closer to an Orwellian society, in which our every action and thought will be controlled by Big Brother.
While we can choose whether or not to put RFID chips in ourselves or our pets, we have little control over tags being placed on commercial products that we buy. In the book "Spychips: How Major Corporations and Government Plan to Track Your Every Move with RFID," Katherine Albrecht and Liz McIntyre describe the most extreme implications of RFID tags. They describe how RFID tags could be used to gauge your spending habits and bank account to determine how much you should be charged for the products you buy. This may sound paranoid, but hackers have proven that some RFID tags can be tampered with, including disabling their anti-theft features and changing the price that corresponds to their product. Better encryption is needed to ensure that hackers can't pick up RFID frequencies with super-sensitive antennae.
What's more, some critics say that relying on RFID as the primary means of security could make human security checkpoints lazy and ineffective. If security guards rely solely on the RFID anti-theft devices in merchandise and RFID technology of government-issued identification to screen for criminals or terrorists, they might miss the criminal activity happening right in front of their eyes.

 

Working of GPS Receivers

A GPS receiver uses satellites to pinpoint locations.

How GPS Receivers Work

Our ancestors had to go to pretty extreme measures to keep from getting lost. They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky.
Things are much, much easier today. For less than $100, you can get a pocket-sized gadget that will tell you exactly where you are on Earth at any moment. As long as you have a GPS receiver and a clear view of the sky, you'll never be lost again.
In this article, we'll find out how these handy guides pull off this amazing trick. As we'll see, the Global Positioning System is vast, expensive and involves a lot of technical ingenuity, but the fundamental concepts at work are quite simple and intuitive.
­When people talk about "a GPS," they usually mean a GPS receiver. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites(24 in operation and three extras in case one fails). The U.S. military developed and implemented this satellite network as a military navigation system, but soon opened it up to everybody else.
Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible" in the sky.
A GPS receiver's job is to locate four or more of these satellites, figure out the distanc­e to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration. Trilateration in three-dimensional space can be a little tricky, so we'll start with an explanation of simple two-dimensional trilateration.

2-D Trilateration

Imagine you are somewhere in the United States and you are TOTALLY lost -- for whatever reason, you have absolutely no clue where you are. You find a friendly local and ask, "Where am I?" He says, "You are 625 miles from Boise, Idaho."
This is a nice, hard fact, but it is not particularly useful by itself. You could be anywhere on a circle around Boise that has a radius of 625 miles, like this:



You ask somebody else where you are, and she says, "You are 690 miles from Minneapolis, Minnesota." Now you're getting somewhere. If you combine this information with the Boise information, you have two circles that intersect. You now know that you must be at one of these two intersection points, if you are 625 miles from Boise and 690 miles from Minneapolis.



If a third person tells you that you are 615 miles from Tucson, Arizona, you can eliminate one of the possibilities, because the third circle will only intersect with one of these points. You now know exactly where you are -- Denver, Colorado.



This same concept works in three-dimensional space, as well, but you're dealing with spheres instead of circles. Next, we'll look at this type of trilateration.

3-D Trilateration

Fundamentally, three-dimensional trilateration isn't much different from two-dimensional trilateration, but it's a little trickier to visualize. Imagine the radii from the previous examples going off in all directions. So instead of a series of circles, you get a series of spheres.
If you know you are 10 miles from satellite A in the sky, you could be anywhere on the surface of a huge, imaginary sphere with a 10-mile radius. If you also know you are 15 miles from satellite B, you can overlap the first sphere with another, larger sphere. The spheres intersect in a perfect circle. If you know the distance to a third satellite, you get a third sphere, which intersects with this circle at two points.
The Earth itself can act as a fourth sphere -- only one of the two possible points will actually be on the surface of the planet, so you can eliminate the one in space. Receivers generally look to four or more satellites, however, to improve accuracy and provide precise altitude information.

In order to make this simple calculation, then, the GPS receiver has to know two things:

• The location of at least three satellites above you


• The distance between you and each of those satellites

The GPS receiver figures both of these things out by analyzing high-frequency, low-power radio signals from the GPS satellites. Better units have multiple receivers, so they can pick up signals from several satellites simultaneously.
Radio waves are electromagnetic energy, which means they travel at the speed of light (about 186,000 miles per second, 300,000 km per second in a vacuum). The receiver can figure out how far the signal has traveled by timing how long it took the signal to arrive

GPS Calculations

On the previous page, we saw that a GPS receiver calculates the distance to GPS satellites by timing a signal's journey from satellite to receiver. As it turns out, this is a fairly elaborate process. At a particular time (let's say midnight), the satellite begins transmitting a long, digital pattern called a pseudo-random code. The receiver begins running the same digital pattern also exactly at midnight. When the satellite's signal reaches the receiver, its transmission of the pattern will lag a bit behind the receiver's playing of the pattern.

A GPS satellite

The length of the delay is equal to the signal's travel time. The receiver multiplies this time by the speed of light to determine how far the signal traveled. Assuming the signal traveled in a straight line, this is the distance from receiver to satellite.
In order to make this measurement, the receiver and satellite both need clocks that can be synchronized down to the nanosecond. To make a satellite positioning system using only synchronized clocks, you would need to have atomic clocks not only on all the satellites, but also in the receiver itself. But atomic clocks cost somewhere between $50,000 and $100,000, which makes them a just a bit too expensive for everyday consumer use.
The Global Positioning System has a clever, effective solution to this problem. Every satellite contains an expensive atomic clock, but the receiver itself uses an ordinary quartz clock, which it constantly resets. In a nutshell, the receiver looks at incoming signals from four or more satellites and gauges its own inaccuracy. In other words, there is only one value for the "current time" that the receiver can use. The correct time value will cause all of the signals that the receiver is receiving to align at a single point in space. That time value is the time value held by the atomic clocks in all of the satellites. So the receiver sets its clock to that time value, and it then has the same time value that all the atomic clocks in all of the satellites have. The GPS receiver gets atomic clock accuracy "for free."
When you measure the distance to four located satellites, you can draw four spheres that all intersect at one point. Three spheres will intersect even if your numbers are way off, but four spheres will not intersect at one point if you've measured incorrectly. Since the receiver makes all its distance measurements using its own built-in clock, the distances will all be proportionally incorrect.
The receiver can easily calculate the necessary adjustment that will cause the four spheres to intersect at one point. Based on this, it resets its clock to be in sync with the satellite's atomic clock. The receiver does this constantly whenever it's on, which means it is nearly as accurate as the expensive atomic clocks in the satellites.
In order for the distance information to be of any use, the receiver also has to know where the satellites actually are. This isn't particularly difficult because the satellites travel in very high and predictable orbits. The GPS receiver simply stores an almanac that tells it where every satellite should be at any given time. Things like the pull of the moon and the sun do change the satellites' orbits very slightly, but the Department of Defense constantly monitors their exact positions and transmits any adjustments to all GPS receivers as part of the satellites' signals.

Differential GPS

So far, we've learned how a GPS receiver calculates its position on earth based on the information it receives from four located satellites. This system works pretty well, but inaccuracies do pop up. For one thing, this method assumes the radio signals will make their way through the atmosphere at a consistent speed (the speed of light). In fact, the Earth's atmosphere slows the electromagnetic energy down somewhat, particularly as it goes through the ionosphere and troposphere. The delay varies depending on where you are on Earth, which means it's difficult to accurately factor this into the distance calculations. Problems can also occur when radio signals bounce off large objects, such as skyscrapers, giving a receiver the impression that a satellite is farther away than it actually is. On top of all that, satellites sometimes just send out bad almanac data, misreporting their own position.
Differential GPS (DGPS) helps correct these errors. The basic idea is to gauge GPS inaccuracy at a stationary receiver station with a known location. Since the DGPS hardware at the station already knows its own position, it can easily calculate its receiver's inaccuracy. The station then broadcasts a radio signal to all DGPS-equipped receivers in the area, providing signal correction information for that area. In general, access to this correction information makes DGPS receivers much more accurate than ordinary receivers.
The most essential function of a GPS receiver is to pick up the transmissions of at least four satellites and combine the information in those transmissions with information in an electronic almanac, all in order to figure out the receiver's position on Earth.
Once the receiver makes this calculation, it can tell you the latitude, longitude and altitude (or some similar measurement) of its current position. To make the navigation more user-friendly, most receivers plug this raw data into map files stored in memory.

The StreetPilot II, a GPS receiver with built-in maps for drivers

You can use maps stored in the receiver's memory, connect the receiver to a computer that can hold more detailed maps in its memory, or simply buy a detailed map of your area and find your way using the receiver's latitude and longitude readouts. Some receivers let you download detailed maps into memory or supply detailed maps with plug-in map cartridges.
A standard GPS receiver will not only place you on a map at any particular location, but will also trace your path across a map as you move. If you leave your receiver on, it can stay in constant communication with GPS satellites to see how your location is changing. With this information and its built-in clock, the receiver can give you several pieces of valuable information:

• How far you've traveled (odometer)


• How long you've been traveling


• Your current speed (speedometer)


• Your average speed


• A "bread crumb" trail showing you exactly where you have traveled on the map


• The estimated time of arrival at your destination if you maintain your current speed

Working of Location Tracing Mechanism

How Location Tracking Works

These days, even traffic lights are keeping an eye on you.

As children playing hide and seek, there seemed to be so many places where we could hide and never be found. With the world bec­oming ever smaller through technology, hiding is increasingly difficult. Cameras peer down on us at red lights, in our workplace, in stores and even at home. Now, those cameras are being augmented by new technologies that track our cars, cell phones and possibly any product we buy.
This location-tracking technology also is being used to streamline supply chains for corporations, seeking to move products to the market faster, and to monitor assets and prevent inventory loss.


­Soon, companies also will be able to track your location. Imagine walking through your local supermarkets, and as you pass through the aisle, an electronic coupon for your favorite cereal is beamed to your phone.
However, many privacy advocates are worried about the implications of these new surveillan­ce systems. Such technology means that marketers and others could know your whereabouts at any time.

Tracking Technology

­ Location tracking is not one, single technology. Rather, it is the convergence of several technologies that can be merged to create systems that track inventory, livestock or ­vehicle fleets. Similar systems can be created to deliver location-based services to wireless devices.
Current technologies being used to create location-tracking and location-based systems include:

• Geographic Information Systems (GIS) - For large-scale location-tracking systems, it is necessary to capture and store geographic information. Geographic information systems can capture, store, analyze and report geographic information.


• Global Positioning System (GPS) - A constellation of 27 Earth-orbiting satellites (24 in operation and three extras in case one fails). A GPS receiver, like the one in your mobile phone, can locate four or more of these satellites, figure out the distance to each, and deduce your location through trilateration. For trilateration to work, it must have a clear line of sight to these four or more satellites. GPS is ideal for outdoor positioning, such as surveying, farming, transportation or military use (for which it was originally designed). See How GPS Receivers Work for more information.
  
  
  
  
  

  Artist's concept of the GPS satellite constellation ­



• Radio Frequency Identification (RFID) - Small, battery-less microchips that can be attached to consumer goods, cattle, vehicles and other objects to track their movements. RFID tags are passive and only transmit data if prompted by a reader. The reader transmits radio waves that activate the RFID tag. The tag then transmits information via a pre-determined radio frequency. This information is captured and transmitted to a central database. Among possible uses for RFID tags are a replacement for traditional UPC bar codes. See How RFIDs Work for more information.


• Wireless Local Area Network (WLAN) - Network of devices that connect via radio frequency, such as 802.11b. These devices pass data over radio waves and provide users with a network with a range of 70 to 300 feet (21.3 to 91.4 meters).

­ Any location tracking or location-based service system will use one or a combination of these technologies. The system requires that a node or tag be placed on the object, animal or person being tracked. For example, the GPS receiver in a cell phone or an RFID tag on a DVD can be used to track those devices with a detection system such as GPS satellites or RFID receivers.
Next , we'll take a look at how location tracking can be used to streamline supply chains and track fleets of trucks, ships and planes.

Types of Tracking

­Companies are finding location-tracking technologies ideal for better managing inventories or fleets of vehicles. Knowing the exact location of each piece of inventory helps to control the supply chain and saves money by not losing those assets that are in transit. Companies, such as retailers, must consider how to track inventory across a wide area, either country or state, and in a smaller area, such as the warehouse or store.
Wide-Area Tracking
On a large scale, companies must track their vehicle fleets across the country or the world. GPS is the ideal tracking technology for tracking over large areas. To do this, every vehicle needs to be equipped with a GPS receiver. As the vehicle crosses the country, the GPS satellites track the truck's position. With GPS, the operator can request positioning at anytime. However, GPS is limited in smaller areas or indoors.
Local-Area and Indoor Tracking
A good example of where GPS would not be suitable for tracking items is in a warehouse or hospitals. The accuracy provided by GPS is not sufficient for such a small scale. Consider all of the medical equipment, wheelchairs, gurneys and even patients that need to be tracked. GPS is not a practical or cost-effective solution.




­For smaller areas, companies and healthcare organizations would likely use a network of RFID tags and readers to monitor the location of assets or inventory. A wireless LAN also would be more suitable. In such a system, each asset would be tagged with an RFID tag, and readers would be placed in strategic locations to be able to accurately read those tags within a matter of inches. A hospital worker would be able to find the exact room a wheelchair is located and retailers would be able to locate an item on any given shelf.
Another example of how this technology is already being deployed is in tracking children in some amusement parks. A child can wear a wristband with an embedded RFID tag. Park staff can track that tag through location receivers positioned around the park. One system in use at Legoland in Denmark even allows for the tag identification number to be registered with the parents' mobile phone.
Location tracking isn't limited to just allowing an organization to know where its assets are, these technologies also will help retailers and marketers find you to better target their key markets.

Location-based Services

­ Mobile phones are becoming more than just a way to call a friend, they are now allowing us to organize our lives, connect to the Internet, shop and take photos. Soon, new lo­cation-based services will be offered as new location-aware technology is rolled out. These location-based services will offer personalized services that are connected the specific location.




New location-based services could set up zones of radio signals that send coupons and other announcements to a consumer's wireless device.

Currently, the most recognized location-based service is the navigation systems found in many new cars. As these technologies advance, it will be easier to find the services you are looking for. For example, if you are looking for an ATM, you just ask for it and the system gives you the location and directions. Other services include traffic advisories and roadside assistance.
On a smaller scale, wireless LANs will be set up in malls and other areas of commerce to locate wireless devices equipped to receive messages. Here is where retailers can send coupons or other offers to your cell phone as you walk through their stores. Shoppers will likely have the choice to opt out of these services.
The success or failure of location-based services largely depends on the roll out of E911 Phase 2 deployment, which is requiring wireless service providers to more accurately locate cell phones in case of emergencies.

Enhanced 911

­ In America, we learn from an early age to call 911 when there's an emergency. When we dial 911, the ­call is automatically forwarded to a public-safety answering point (PSAP), also called a 911 call center. When the call is answered, the 911 operator is provided with automatic location information (ALI), pinpointing the exact position of the call. Today, many areas also have Enhanced 911 (E-911), which allows a PSAP to determine the general location from where the call originated, but cannot yet pinpoint the location.



According to the Cellular Telephone Industry Association (CTIA), 150,000 emergency wireless calls are made in the United States each day. The government has stepped in to ensure that E-911 capabilities are improved. New technologies being developed by wireless service providers at the demand of the Federal Communications Commission are expected to enhance the location-finding ability of E-911 to locate the exact position of a wireless emergency call.
The FCC is rolling out E-911 in phases:

• Phase 0 - This is the basic 911 process. Wireless calls are sent to a PSAP. Service providers must direct a call to a PSAP even if the caller is not a subscriber to their service.


• Phase I - The FCC's rule requires that a phone number display with each wireless 911 call, allowing the PSAP operator to call back if there is a disconnection.


• Phase II - The final phase requires carriers to place GPS receivers in phones in order to deliver more specific latitude and longitude location information. Location information must be accurate within 164 to 984 feet (50-300 meters).

Without Phase II, a caller's location can only be narrowed down to the cell from which the call originated. When Phase II is implemented, a cell-phone user's phone number, or Automatic Number Identification (ANI), and the address and location of the receiving-antenna site will be sent to the E-911 Tandem, the switch that routes 911 calls to the appropriate PSAP based on the ANI-defined geographic location. Once the caller's voice and ANI are transferred to the PSAP, the PSAP operator will be able to view a graphic display that shows the longitude and latitude of the person as accessed through GPS satellites. The operator's computer will link to the ALI database, which stores address data and other information.
The implementation of Phase II technology introduces new commercial opportunities. As mentioned in the previous section, location-based services will leverage the infrastructure of E-911 technology to deliver commercial services to phones, including advertising. These new technologies also create concerns over privacy, which we will examine in the next section.

Why 911? Have you ever wondered why 911 was chosen as the universal emergency code in the United States? Prior to the 1960s, there was no universal number to call for emergency help. In 1967, the Federal Communications Commission met with AT&T to establish such a number, according to the National Emergency Number Association (NENA). But why did they choose 911? Why not 422 or 111? There are several reasons why 911 was chosen. It's a short, easy to remember number, but more importantly, 911 was a unique number -- it had never been designated for an office code, area code or service code.

On February 16, 1968, Alabama Senator Rankin Fite made the first 911 call in the United States in Haleyville, Alabama. The Alabama Telephone Company carried the call. A week later, Nome, Alaska, implemented a 911 system. In 1973, the White House's Office of Telecommunication issued a national statement supporting the use of 911 and pushed for the establishment of a Federal Information Center to assist government agencies in implementing the system.

Location and Tracking Privacy

­ The words location tracking can lead many to worry about privacy. Some may worry about the government knowing t­heir whereabouts, stalkers spying on them or even a spouse monitoring their movements. Although the technology could allow anyone to find you at any given moment, measures are being taken to prevent this kind of abuse.
Wireless companies are ensuring consumers that federal law prevents these scenarios from happening. In 1999, the U.S. Congress amended the Communications Act of 1934 to include a privacy provision by adding section 222, which states:

222 (a)Every telecommunications carrier has a duty to protect the confidentiality of proprietary information of, and relating to ... customers ... (b)A telecommunications carrier that receives or obtains proprietary information from another carrier for purposes of providing any telecommunications service shall use such information only for such purpose, and shall not use such information for its own marketing efforts.
(c )(1) PRIVACY REQUIREMENTS FOR TELECOMMUNICATIONS CARRIERS. - Except as required by law or with the approval of the customer, a telecommunications carrier that receives or obtains customer proprietary network information by virtue of its provision of a telecommunications service shall only use, disclose, or permit access to individually identifiable customer proprietary network information in its provision of (A) the telecommunications service from which such information is derived, or (B) services necessary to, or used in, the provision of such telecommunications service, including the publishing of directories. (2) DISCLOSURE ON REQUEST BY CUSTOMERS. - A telecommunications carrier shall disclose customer proprietary network information, upon affirmative written request by the customer, to any person designated by the customer.

This provision is intended to protect consumers' information from being given out. However, consumers must decide how much privacy they are willing to trade for the conveniences and benefits offered by location-tracking technology.

 

 

Working of Facial Recognition Systems

How Facial Recognition Systems Work

Anyone who has seen the TV show "Las Vegas" has seen facial recognition software in action. In any given episode, the security department at the fictional Montecito Hotel and Casino uses its video surveillance system to pull an image of a card counter, thief or blacklisted individual. It then runs that image through the database to find a match and identify the person. By the end of the hour, all bad guys are escorted from the casino or thrown in jail. But what looks so easy on TV doesn't always translate as well in the real world.

In 2001, the Tampa Police Department installed police cameras equipped with facial recognition technology in their Ybor City nightlife district in an attempt to cut down on crime in the area. The system failed to do the job, and it was scrapped in 2003 due to ineffectiveness. People in the area were seen wearing masks and making obscene gestures, prohibiting the cameras from getting a clear enough shot to identify anyone.
Boston's Logan Airport also ran two separate tests of facial recognition systems at its security checkpoints using volunteers. Over a three month period, the results were disappointing. According to the Electronic Privacy Information Center, the system only had a 61.4 percent accuracy rate, leading airport officials to pursue other security options.
Humans have always had the innate ability to recognize and distinguish between faces, yet computers only recently have shown the same ability. In the mid 1960s, scientists began work on using the computer to recognize human faces. Since then, facial recognition software has come a long way.
In this article, we will look at the history of facial recognition systems, the changes that are being made to enhance their capabilities and how governments and private companies use (or plan to use) them.

Facial Recognition Technology

FaceIt software compares the faceprint with other images in the database.

­Identix®, a company based in Minnesota, is one of many developers of facial recognition technology. Its software, FaceIt®, can pick someone's face out of a crowd, extract the face from the rest of the scene and compare it to a database of stored images. In order for this software to work, it has to know how to differentiate between a basic face and the rest of the background. Facial recognition software is based on the ability to recognize a face and then measure the various features of the face.
Every face has numerous, distinguishable landmarks, the different peaks and valleys that make up facial features. FaceIt defines these landmarks as nodal points. Each human face has approximately 80 nodal points. Some of these measured by the software are:

• Distance between the eyes
• Width of the nose
• Depth of the eye sockets
• The shape of the cheekbones
• The length of the jaw line

These nodal points are measured creating a numerical code, called a faceprint, representing the face in the database.In the past, facial recognition software has relied on a 2D image to compare or identify another 2D image from the database. To be effective and accurate, the image captured needed to be of a face that was looking almost directly at the camera, with little variance of light or facial expression from the image in the database. This created quite a problem.
In most instances the images were not taken in a controlled environment. Even the smallest changes in light or orientation could reduce the effectiveness of the system, so they couldn't be matched to any face in the database, leading to a high rate of failure.

3D Facial Recognition

The Vision 3D + 2D ICAO camera is used to perform enrollment, verification and identification of 3D and 2D face images.

A newly-emerging trend in facial recognition software uses a 3D model, which claims to provide more accuracy. Capturing a real-time 3D image of a person's facial surface, 3D facial recognition uses distinctive features of the face -- where rigid tissue and bone is most apparent, such as the curves of the eye socket, nose and chin -- to identify the subject. These areas are all unique and don't change over time.
Using depth and an axis of measurement that is not affected by lighting, 3D facial recognition can even be used in darkness and has the ability to recognize a subject at different view angles with the potential to recognize up to 90 degrees (a face in profile).
Using the 3D software, the system goes through a series of steps to verify the identity of an individual.
Detection
Acquiring an image can be accomplished by digitally scanning an existing photograph (2D) or by using a video image to acquire a live picture of a subject (3D).
Alignment
Once it detects a face, the system determines the head's position, size and pose. As stated earlier, the subject has the potential to be recognized up to 90 degrees, while with 2D, the head must be turned at least 35 degrees toward the camera.
Measurement
The system then measures the curves of the face on a sub-millimeter (or microwave) scale and creates a template.


Representation
The system translates the template into a unique code. This coding gives each template a set of numbers to represent the features on a subject's face.
Matching
If the image is 3D and the database contains 3D images, then matching will take place without any changes being made to the image. However, there is a challenge currently facing databases that are still in 2D images. 3D provides a live, moving variable subject being compared to a flat, stable image. New technology is addressing this challenge. When a 3D image is taken, different points (usually three) are identified. For example, the outside of the eye, the inside of the eye and the tip of the nose will be pulled out and measured. Once those measurements are in place, an algorithm (a step-by-step procedure) will be applied to the image to convert it to a 2D image. After conversion, the software will then compare the image with the 2D images in the database to find a potential match.
Verification or Identification
In verification, an image is matched to only one image in the database (1:1). For example, an image taken of a subject may be matched to an image in the Department of Motor Vehicles database to verify the subject is who he says he is. If identification is the goal, then the image is compared to all images in the database resulting in a score for each potential match (1:N). In this instance, you may take an image and compare it to a database of mug shots to identify who the subject is.

Biometric Facial Recognition

The image may not always be verified or identified in facial recognition alone. Identix® has created a new product to help with precision. The development of FaceIt®Argus uses skin biometrics, the uniqueness of skin texture, to yield even more accurate results.

The surface texture analysis (STA) algorithm operates on the top percentage of results as determined by the local feature analysis. STA creates a skinprint and performs either a 1:1 or 1:N match depending on whether you're looking for verification or identification.

The process, called Surface Texture Analysis, works much the same way facial recognition does. A picture is taken of a patch of skin, called a skinprint. That patch is then broken up into smaller blocks. Using algorithms to turn the patch into a mathematical, measurable space, the system will then distinguish any lines, pores and the actual skin texture. It can identify differences between identical twins, which is not yet possible using facial recognition software alone. According to Identix, by combining facial recognition with surface texture analysis, accurate identification can increase by 20 to 25 percent.
FaceIt currently uses three different templates to confirm or identify the subject: vector, local feature analysis and surface texture analysis.

• The vector template is very small and is used for rapid searching over the entire database primarily for one-to-many searching.
• The local feature analysis (LFA) template performs a secondary search of ordered matches following the vector template.
• The surface texture analysis (STA) is the largest of the three. It performs a final pass after the LFA template search, relying on the skin features in the image, which contains the most detailed information.

By combining all three templates, FaceIt® has an advantage over other systems. It is relatively insensitive to changes in expression, including blinking, frowning or smiling and has the ability to compensate for mustache or beard growth and the appearance of eyeglasses. The system is also uniform with respect to race and gender.

Poor lighting can make it more difficult for facial recognition software to verify or identify someone.

However, it is not a perfect system. There are some factors that could get in the way of recognition, including:

• Significant glare on eyeglasses or wearing sunglasses
• Long hair obscuring the central part of the face
• Poor lighting that would cause the face to be over- or under-exposed
• Lack of resolution (image was taken too far away)

Identix isn't the only company with facial recognition systems available. While most work the same way FaceIt does, there are some variations. For example, a company called Animetrix, Inc. has a product called FACEngine ID® SetLight that can correct lighting conditions that cannot normally be used, reducing the risk of false matches. Sensible Vision, Inc. has a product that can secure a computer using facial recognition. The computer will only power on and stay accessible as long as the correct user is in front of the screen. Once the user moves out of the line of sight, the computer is automatically secured from other users.
Due to these strides in technology, facial and skin recognition systems are more widely used than just a few years ago.Next, we'll look at where and how they are being used and what's in store for the future.

Facial Recognition Systems Uses

In the past, the primary users of facial recognition software have been law enforcement agencies, who used the system to capture random faces in crowds. Some government agencies have also been using the systems for security and to eliminate voter fraud. The U.S. government has recently begun a program called US-VISIT (United States Visitor and Immigrant Status Indicator Technology), aimed at foreign travelers gaining entry to the United States. When a foreign traveler receives his visa, he will submit fingerprints and have his photograph taken. The fingerprints and photograph are checked against a database of known criminals and suspected terrorists. When the traveler arrives in the United States at the port of entry, those same fingerprints and photographs will be used to verify that the person who received the visa is the same person attempting to gain entry.

Jim Williams, head of US-VISIT, former Secretary Tom Ridge and former Commissioner Robert Bonner launch US-VISIT in Atlanta, Georgia.

However, there are now many more situations where the software is becoming popular. As the systems become less expensive, making their use more widespread. They are now compatible with cameras and computers that are already in use by banks and airports. The TSA is currently working on and testing out its Registered Traveler program. The program will provide speedy security screening for passengers who volunteer information and complete a security threat assessment. At the airport there will be specific lines for the Registered Traveler to go through that will move more quickly, verifying the traveler by their facial features.
Other potential applications include ATM and check-cashing security. The software is able to quickly verify a customer's face. After a customer consents, the ATM or check-cashing kiosk captures a digital image of him. The FaceIt software then generates a faceprint of the photograph to protect customers against identity theft and fraudulent transactions. By using the facial recognition software, there's no need for a picture ID, bankcard or personal identification number (PIN) to verify a customer's identity. This way businesses can prevent fraud from occurring.

Time Tracking A4Vision, a creator of facial recognition software, is currently marketing a system that will keep track of employees' time and attendance. Their Web site states that it will prohibit "buddy punching," which will cut down on security risks and decreased productivity.

While all the examples above work with the permission of the individual, not all systems are used with your knowledge. In the first section we mentioned that systems were used during the Super Bowl by the Tampa Police, and in Ybor City. These systems were taking pictures of all visitors without their knowledge or their permission. Opponents of the systems note that while they do provide security in some instances, it is not enough to override a sense of liberty and freedom. Many feel that privacy infringement is too great with the use of these systems, but their concerns don't end there. They also point out the risk involved with identity theft. Even facial recognition corporations admit that the more use the technology gets, the higher the likelihood of identity theft or fraud.
As with many developing technologies, the incredible potential of facial recognition comes with some drawbacks, but manufacturers are striving to enhance the usability and accuracy of the systems.

 

Working of Fingerprint Scanners

How Fingerprint Scanners Work

A computer mouse with a built-in fingerprint scanner

Computerized fingerprint scanners have been a mainstay of spy thrillers for decades, but up until recently, they were pretty exotic technology in the real world. In the past few years, however, scanners have started popping up all over the place -- in police stations, high-security buildings and even on PC keyboards. You can pick up a personal USB fingerprint scanner for less than $100, and just like that, your computer's guarded by high-tech biometrics. Instead of, or in addition to, a password, you need your distinctive print to gain access. In this article, we'll examine the secrets behind this exciting development in law enforcement and identity security. We'll also see how fingerprint scanner security systems stack up to conventional password and identity card systems, and find out how they can fail.

 

Fingerprint Basics

Fingerprints are one of those bizarre twists of nature. Human beings happen to have built-in, easily accessible identity cards. You have a unique design, which represents you alone, literally at your fingertips. How did this happen? People have tiny ridges of skin on their fingers because this particular adaptation was extremely advantageous to the ancestors of the human species. The pattern of ridges and "valleys" on fingers make it easier for the hands to grip things, in the same way a rubber tread pattern helps a tire grip the road.

The other function of fingerprints is a total coincidence. Like everything in the human body, these ridges form through a combination of genetic and environmental factors. The genetic code in DNA gives general orders on the way skin should form in a developing fetus, but the specific way it forms is a result of random events. The exact position of the fetus in the womb at a particular moment and the exact composition and density of surrounding amniotic fluid decides how every individual ridge will form.
So, in addition to the countless things that go into deciding your genetic make-up in the first place, there are innumerable environmental factors influencing the formation of the fingers. Just like the weather conditions that form clouds or the coastline of a beach, the entire development process is so chaotic that, in the entire course of human history, there is virtually no chance of the same exact pattern forming twice.
Consequently, fingerprints are a unique marker for a person, even an identical twin. And while two prints may look basically the same at a glance, a trained investigator or an advanced piece of software can pick out clear, defined differences.
This is the basic idea of fingerprint analysis, in both crime investigation and security. A fingerprint scanner's job is to take the place of a human analyst by collecting a print sample and comparing it to other samples on record. Next , we'll find out how scanners do this.

Optical Scanner

A fingerprint scanner system has two basic jobs -- it needs to get an image of your finger, and it needs to determine whether the pattern of ridges and valleys in this image matches the pattern of ridges and valleys in pre-scanned images. There are a number of different ways to get an image of somebody's finger. The most common methods today are optical scanning and capacitance scanning. Both types come up with the same sort of image, but they go about it in completely different ways.
The heart of an optical scanner is a charge coupled device (CCD), the same light sensor system used in digital cameras and camcorders. A CCD is simply an array of light-sensitive diodes called photosites, which generate an electrical signal in response to light photons. Each photosite records a pixel, a tiny dot representing the light that hit that spot. Collectively, the light and dark pixels form an image of the scanned scene (a finger, for example). Typically, an analog-to-digital converter in the scanner system processes the analog electrical signal to generate a digital representation of this image. See How Digital Cameras Work for details on CCDs and digital conversion.
The scanning process starts when you place your finger on a glass plate, and a CCD camera takes a picture. The scanner has its own light source, typically an array of light-emitting diodes, to illuminate the ridges of the finger. The CCD system actually generates an inverted image of the finger, with darker areas representing more reflected light (the ridges of the finger) and lighter areas representing less reflected light (the valleys between the ridges).
Before comparing the print to stored data, the scanner processor makes sure the CCD has captured a clear image. It checks the average pixel darkness, or the overall values in a small sample, and rejects the scan if the overall image is too dark or too light. If the image is rejected, the scanner adjusts the exposure time to let in more or less light, and then tries the scan again.
If the darkness level is adequate, the scanner system goes on to check the image definition (how sharp the fingerprint scan is). The processor looks at several straight lines moving horizontally and vertically across the image. If the fingerprint image has good definition, a line running perpendicular to the ridges will be made up of alternating sections of very dark pixels and very light pixels.
If the processor finds that the image is crisp and properly exposed, it proceeds to comparing the captured fingerprint with fingerprints on file. We'll look at this process in a minute, but first we'll examine the other major scanning technology, the capacitive scanner.

Capacitance Scanner

Like optical scanners, capacitive fingerprint scanners generate an image of the ridges and valleys that make up a fingerprint. But instead of sensing the print using light, the capacitors use electrical current. The diagram below shows a simple capacitive sensor. The sensor is made up of one or more semiconductor chips containing an array of tiny cells. Each cell includes two conductor plates, covered with an insulating layer. The cells are tiny -- smaller than the width of one ridge on a finger.

The sensor is connected to an integrator, an electrical circuit built around an inverting operational amplifier. The inverting amplifier is a complex semiconductor device, made up of a number of transistors, resistors and capacitors. The details of its operation would fill an entire article by itself, but here we can get a general sense of what it does in a capacitance scanner.
Like any amplifier, an inverting amplifier alters one current based on fluctuations in another current . Specifically, the inverting amplifier alters a supply voltage. The alteration is based on the relative voltage of two inputs, called the inverting terminal and the non-inverting terminal. In this case, the non-inverting terminal is connected to ground, and the inverting terminal is connected to a reference voltage supply and a feedback loop. The feedback loop, which is also connected to the amplifier output, includes the two conductor plates.
As you may have recognized, the two conductor plates form a basic capacitor, an electrical component that can store up charge . The surface of the finger acts as a third capacitor plate, separated by the insulating layers in the cell structure and, in the case of the fingerprint valleys, a pocket of air. Varying the distance between the capacitor plates (by moving the finger closer or farther away from the conducting plates) changes the total capacitance (ability to store charge) of the capacitor. Because of this quality, the capacitor in a cell under a ridge will have a greater capacitance than the capacitor in a cell under a valley.
To scan the finger, the processor first closes the reset switch for each cell, which shorts each amplifier's input and output to "balance" the integrator circuit. When the switch is opened again, and the processor applies a fixed charge to the integrator circuit, the capacitors charge up. The capacitance of the feedback loop's capacitor affects the voltage at the amplifier's input, which affects the amplifier's output. Since the distance to the finger alters capacitance, a finger ridge will result in a different voltage output than a finger valley.
The scanner processor reads this voltage output and determines whether it is characteristic of a ridge or a valley. By reading every cell in the sensor array, the processor can put together an overall picture of the fingerprint, similar to the image captured by an optical scanner.
The main advantage of a capacitive scanner is that it requires a real fingerprint-type shape, rather than the pattern of light and dark that makes up the visual impression of a fingerprint. This makes the system harder to trick. Additionally, since they use a semiconductor chip rather than a CCD unit, capacitive scanners tend to be more compact that optical devices.

Analysis

In movies and TV shows, automated fingerprint analyzers typically overlay various fingerprint images to find a match. In actuality, this isn't a particularly practical way to compare fingerprints. Smudging can make two images of the same print look pretty different, so you're rarely going to get a perfect image overlay. Additionally, using the entire fingerprint image in comparative analysis uses a lot of processing power, and it also makes it easier for somebody to steal the print data. Instead, most fingerprint scanner systems compare specific features of the fingerprint, generally known as minutiae. Typically, human and computer investigators concentrate on points where ridge lines end or where one ridge splits into two (bifurcations). Collectively, these and other distinctive features are sometimes called typica.
The scanner system software uses highly complex algorithms to recognize and analyze these minutiae. The basic idea is to measure the relative positions of minutiae, in the same sort of way you might recognize a part of the sky by the relative positions of stars. A simple way to think of it is to consider the shapes that various minutia form when you draw straight lines between them. If two prints have three ridge endings and two bifurcations, forming the same shape with the same dimensions, there's a high likelihood they're from the same print.
To get a match, the scanner system doesn't have to find the entire pattern of minutiae both in the sample and in the print on record, it simply has to find a sufficient number of minutiae patterns that the two prints have in common. The exact number varies according to the scanner programming.

Pros and Cons

There are several ways a security system can verify that somebody is an authorized user. Most systems are looking for one or more of the following:

• What you have
• What you know
• Who you are

To get past a "what you have" system, you need some sort of "token," such as an identity card with a magnetic strip. A "what you know" system requires you to enter a password or PIN number. A "who you are" system is actually looking for physical evidence that you are who you say you are -- a specific fingerprint, voice or iris pattern.
"Who you are" systems like fingerprint scanners have a number of advantages over other systems. To name few:

• Physical attributes are much harder to fake than identity cards.
• You can't guess a fingerprint pattern like you can guess a password.
• You can't misplace your fingerprints, irises or voice like you can misplace an access card.
• You can't forget your fingerprints like you can forget a password.

But, as effective as they are, they certainly aren't infallible, and they do have major disadvantages. Optical scanners can't always distinguish between a picture of a finger and the finger itself, and capacitive scanners can sometimes be fooled by a mold of a person's finger. If somebody did gain access to an authorized user's prints, the person could trick the scanner. In a worst-case scenario, a criminal could even cut off somebody's finger to get past a scanner security system. Some scanners have additional pulse and heat sensors to verify that the finger is alive, rather than a mold or dismembered digit, but even these systems can be fooled by a gelatin print mold over a real finger. (This site explains various ways somebody might trick a scanner.)
To make these security systems more reliable, it's a good idea to combine the biometric analysis with a conventional means of identification, such as a password (in the same way an ATM requires a bank card and a PIN code).
The real problem with biometric security systems is the extent of the damage when somebody does manage to steal the identity information. If you lose your credit card or accidentally tell somebody your secret PIN number, you can always get a new card or change your code. But if somebody steals your fingerprints, you're pretty much out of luck for the rest of your life. You wouldn't be able to use your prints as a form of identification until you were absolutely sure all copies had been destroyed. There's no way to get new prints.
But even with this significant drawback, fingerprint scanners and biometric systems are an excellent means of identification. In the future, they'll most likely become an integral part of most peoples' everyday life, just like keys, ATM cards and passwords are today.