Beyond the Door

Multispectral imaging opens the door of biometrics

• By Phil Scarfo
• Mar 01, 2011

For many years now, the promise of biometrics has not been fully realized. This is, in large part, because performance in the lab is not representative of performance in the field. That’s the reason major programs for Citizen ID and others have never really been fulfilled.

The core problem is that conventional biometric technologies rely on unobstructed and complete contact between the fingerprint and the sensor, an elusive condition in the real world, a world that is wet or dry and dirty, and users are not all young office workers with great skin who are experienced at using biometrics.

Wet Fingers Fail
Wet conditions are notoriously difficult for both semiconductor and conventional optical fingerprint sensors to handle, and yet moisture is a fairly common realworld condition. Some environments are naturally damp, due to climate (London) or setting (a spa). Some people simply have moist hands. It also is typical for people going through security to be nervous -- and thus have sweaty hands.

Conventional optical technologies are often unable to produce images in such wet conditions because excess moisture obscures fingerprint ridges, resulting in images of puddles, not fingerprints.

Dryness Is a Major Problem
Has any other real-world condition caused so much trouble in the biometrics industry? Dry fingertips are common, caused by, among other things, climate conditions, natural skin characteristics, frequent hand-washing and air travel. For instance, a high-desert climate causes dry fingers in an entire population.

Most optical sensors are configured to look for the presence or absence of total internal reflectance (TIR), which is the phenomenon whereby the interface between glass and air acts like a mirror at certain angles. The contact between the skin and the platen defeats the TIR, allowing those points of contact between the finger and the sensor to be imaged. Thus, those points of contact must be complete and unobscured to enable the conventional sensor to collect a fingerprint image.

With dry fingers, establishing firm and complete contact with the sensor is difficult. There is not enough moisture in the skin, nor is the skin pliable enough to facilitate the contact necessary for TIR imaging.

It’s a Dirty World Out There
The real world is a rough place, and most of us are showing some wear and tear on our hands. Additionally, people don’t have time to wash and lotion their hands each time they use a fingerprint sensor.

A construction site is an interesting real-world case. Construction workers work with their hands and have the cuts and calluses to prove it. Additionally, the construction site is dirty, so workers may have grime on their hands when they approach a fingerprint sensor. Altogether, this real-world scenario is a nightmare for system administrators whose conventional fingerprint sensors depend on quality contact between the finger and the platen.

We’re All Different
Many people, both young and adult, have small or fine fingerprint features that can be difficult to image. If the sensor cannot differentiate between these fine characteristics, system performance will suffer.

Age is another physiological characteristic that can affect a sensor’s effectiveness. One effect of aging is the loss of collagen in the skin; elderly fingers have soft fingerprint ridges that collapse into one another when the finger touches a surface.

Because many sensor technologies depend on the quality of contact between the finger and the sensor to collect a good image, soft fingerprint ridges can be difficult.

There are behavioral differences across user populations that also can affect performance. People have different levels of experience with technology and biometrics, and this affects how each person approaches the fingerprint sensor. For example, some people may tend to press hard, and others, being more tentative, may barely touch the sensor at all. For technologies that depend on the quality of that touch, this can be a big problem.

You Don’t Want to Get “Spoofed”
Being able to discriminate a real finger from an imposter or “spoof” fingerprint is extremely important. Access -- through national borders, into buildings or physical plants, and into electronic devices such as PCs and networks -- is increasingly unsupervised. Nonetheless, security, labor costs and convenience often necessitate the use of biometric access control methods such as fingerprint verification.

Ridges are easy to imitate using common household products and ingredients. A variety of materials, from the inexpensive to the sophisticated, can be used to circumvent traditional fingerprint identification systems. Some of these materials are so thin and colorless that they can even be used, undetected, in access control environments that have trained attendants. For example, a gummy bear candy that costs a few cents can make a very accurate fingerprint that will spoof a traditional fingerprint.

Overcoming Common Obstacles
Multispectral imaging is a sophisticated technology developed to overcome the fingerprint-capture problems that plague conventional imaging systems in lessthan- ideal conditions. This more-effective solution is based on using multiple spectrums of light and advanced polarization techniques to extract unique fingerprint characteristics from both the surface and subsurface of the skin. The nature of human skin physiology is such that this subsurface information is both relevant to fingerprint capture and unaffected by surface wear and other environmental factors.

The fingerprint ridges that we see on the surface of the finger have their foundation beneath the surface of the skin, in the capillary beds and other sub-dermal structures. The fingerprint ridges we see on our fingertips are merely an echo of the foundational “inner fingerprint.”

Unlike the surface fingerprint characteristics that can be obscured by moisture, dirt or wear, the inner fingerprint lies undisturbed and unaltered beneath the surface. When surface fingerprint information is combined with subsurface fingerprint information and reassembled in an intelligent and integrated manner, the results are more consistent, more inclusive and more tamper-resistant.

Multispectral imaging technology also can detect living flesh from other organic or synthetic materials. Liveness detection is built from cutting-edge machine “learning” algorithms. Using these algorithms and the wealth of information available from multispectral fingerprint images, liveness detection capabilities can be updated if new methods of spoofing are identified. Unlike any other fingerprint technology, this learning capability allows multispectral imaging sensors to keep up with new threats. The inexpensive and readily available films and prostheses that easily defeat conventional fingerprint devices are rendered ineffective against this technology.

What Does All This Mean?
For some time, biometrics have been limited primarily to door types of applications -- ingress/egress, time and attendance, and similar tasks -- because of the problems of traditional biometric technologies. Some organizations have gone so far as to use a PIN bypass if the biometric reader is having problems, defeating the whole purpose of having a biometric.

On the contrary, multispectral fingerprint sensors capture high-quality images because the direct imaging process does not depend on a clean finger/sensor interface.

With this technology, biometrics finally can provide the same type of reliability as a card without all the negatives of the card, including the cost of the cards themselves and the greater cost of managing them. After all, nobody leaves his finger at home, nor does it wear out.

More importantly, biometrics, which determines that you are you, not what you carry, can now be used in more places and more applications.

Government. For example, the government uses the technology in its Transportation Worker Identity Credential. More than 40 million people are already enrolled on multispectral imaging-based systems at locales ranging from the classic door access-control situation to the gates of the world’s favorite theme parks.

Such readers also are keeping borders secure around the world. Indeed, more than 400,000 people pass through multispectral imaging sensors every day at the Hong Kong border crossing.

Healthcare. Most importantly, though, multispectral imaging provides reliable identity verification in settings beyond the door. For instance, CareFusion (formally a division of Cardinal Health) provide secure medical drug dispensing equipment.

As an experienced user and client of biometrics, CareFusion understood technology’s challenges. After an extensive industrywide evaluation of biometrics offerings devices, CareFusion selected multispectral imaging fingerprint sensors and software for integration into its latest generation of dispensing cabinets.

Results have been outstanding. The performance of multispectral imaging in to MedStation 4000 has clearly demonstrated a dramatic decrease in failure rates and other performance problems experienced with conventional biometric devices. With multispectral imaging, the system’s failure to enroll and failure to acquire has dropped to virtually zero. Where in the past, the solution was effective only about 80 percent of the time for four out of five users, the new MedStation 4000 performance is nearly perfect.

E-prescribing drugs. E-prescribing enables a physician to prescribe medication via a computer or mobile device. These systems are typically integrated with electronic medical records and help prevent harmful drug interactions and incorrect dosing.

The Drug Enforcement Administration issued a new rule requiring doctors and pharmacists to use two-factor authentication when electronically prescribing controlled substances.

The doctor or pharmacist creating the prescription must authenticate, according the DEA, with two of the following: “something you know (a knowledge factor), something you have (a hard token stored separately from the computer being accessed), and something you are (biometric information). Ohio already has a similar rule in place, which always requires a second factor. The state essentially has adopted biometrics as that second form.

A challenge with fingerprint biometrics in this environment is that healthcare workers frequently wear rubber gloves. They must remove the gloves to present the biometric, and the ongoing use of the gloves can dry out the skin, making it difficult to get a good fingerprint scan. Since multispectral technology captures the fingerprint data from beneath the surface of the skin, it can read the fingerprint, regardless of the dry skin.

Micro-banking. For a country such as India, where the government is looking to provide services to an entire subcontinent’s citizens and commercial entities want to reach out to the poor, especially those who have been excluded because of limited technology, multispectral imaging-based biometrics is turning visions into realities.

In India, Analogics Tech India provides reliable fingerprint biometric solutions leveraging multispectral imaging for prestigious customers, including TCS, Bartronics, ESSL, WIPRO and AGS. The company’s multispectral imaging sensor-based handheld readers are used in financial inclusion or rural banking applications where banking services, such as opening savings accounts, transferring funds, making deposits, withdrawing cash and obtaining loans are taken to the poor and needy in remote rural areas, where citizens otherwise have no access to banks.

Bank of India, Karnataka Bank, State Bank of Hyderabad, and State Bank of Bikaner and Jaipur are all leveraging the technology.

Multispectral imaging sensors also are used in biometric ATMs and handhelds that act like micro-ATMs. These sensors are used in rural employmentguarantee programs where fingerprintbased biometric cards are used by beneficiaries to withdraw their weekly wages. Multispectral imaging-based handhelds are used in public distribution systems and education projects where the biometric is used by citizens for collecting rations and for the authentication of students’ time and attendance reporting.

Similar applications are now be undertaken for getting on a company’s data network, operating a forklift, signing for merchandise, creating major Citizen ID programs and virtually every type of application in which organizations now feel forced to use cards, keys or PINs. Multispectral imaging is making the deployment of functional, useful biometrics a reality.

This article originally appeared in the March 2011 issue of Security Today.