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
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
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
The Drug Enforcement Administration issued a new rule requiring doctors and
pharmacists to use two-factor authentication when electronically prescribing controlled
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
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
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
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
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.
Philip J. Scarfo is vice president of worldwide sales and marketing at Lumidigm.