Fingerprint biometrics

Principles of fingerprint biometrics

A fingerprint is made of a a number of ridges and valleys on the surface of the finger. Ridges are the upper skin layer segments of the finger and valleys are the lower segments. The ridges form so-called minutia points: ridge endings (where a ridge end) and ridge bifurcations (where a ridge splits in two). Many types of minutiae exist, including dots (very small ridges), islands (ridges slightly longer than dots, occupying a middle space between two temporarily divergent ridges), ponds or lakes (empty spaces between two temporarily divergent ridges), spurs (a notch protruding from a ridge), bridges (small ridges joining two longer adjacent ridges), and crossovers (two ridges which cross each other).

The uniqueness of a fingerprint can be determined by the pattern of ridges and furrows as well as the minutiae points. There are five basic fingerprint patterns: arch, tented arch, left loop, right loop and whorl. Loops make up 60% of all fingerprints, whorls account for 30%, and arches for 10%.

Issues with fingerprint systems
The tip of the finger is a small area from which to take measurements, and ridge patterns can be affected by cuts, dirt, or even wear and tear. Acquiring high-quality images of distinctive fingerprint ridges and minutiae is complicated task.

People with no or few minutia points (surgeons as they often wash their hands with strong detergents, builders, people with special skin conditions) cannot enroll or use the system. The number of minutia points can be a limiting factor for security of the algorithm. Results can also be confused by false minutia points (areas of obfuscation that appear due to low-quality enrollment, imaging, or fingerprint ridge detail).

Note: There is some controversy over the uniqueness of fingerprints. The quality of partial prints is however the limiting factor. As the number of defining points of the fingerprint become smaller, the degree of certainty of identity declines. There have been a few well-documented cases of people being wrongly accused on the basis of partial fingerprints.

Benefits of fingerprint biometric systems
Easy to use
Cheap
Small size
Low power
Non-intrusive
Large database already available

Applications of fingerprint biometrics
Fingerprint sensors are best for devices such as cell phones, USB flash drives, notebook computers and other applications where price, size, cost and low power are key requirements. Fingerprint biometric systems are also used for law enforcement, background searches to screen job applicants, healthcare and welfare.
Fingerprints are usually considered to be unique, with no two fingers having the exact same dermal ridge characteristics.

How does fingerprint biometrics work
The main technologies used to capture the fingerprint image with sufficient detail are optical, silicon, and ultrasound.

There are two main algorithm families to recognize fingerprints:

Minutia matching compares specific details within the fingerprint ridges. At registration (also called enrollment), the minutia points are located, together with their relative positions to each other and their directions. At the matching stage, the fingerprint image is processed to extract its minutia points, which are then compared with the registered template.

Pattern matching compares the overall characteristics of the fingerprints, not only individual points. Fingerprint characteristics can include sub-areas of certain interest including ridge thickness, curvature, or density. During enrollment, small sections of the fingerprint and their relative distances are extracted from the fingerprint. Areas of interest are the area around a minutia point, areas with low curvature radius, and areas with unusual combinations of ridges.

Biometrics

What is “biometrics”?

Biometrics is a field of security and identification technology based on the measurement of unique physical characteristics such as fingerprints, retinal patterns, and facial structure. To verify an individual's identity, biometric devices scan certain characteristics and compare them with a stored entry in a computer database. While the technology goes back years and has been used in highly sensitive institutions such as defense and nuclear facilities, the proliferation of electronic data exchange generated new demand for biometric applications that can secure electronically stored data and online transactions.

Biometrics is the practice of automatically identifying people by one or more physical characteristics.

TYPES OF BIOMETRIC SYSTEMS

FINGERPRINTS.
Fingerprint-based biometric systems scan the dimensions, patterns, and topography of fingers, thumbs, and palms. The most common biometric in forensic and governmental databases, fingerprints contain up to 60 possibilities for minute variation, and extremely large and increasingly integrated networks of these stored databases already exist. The largest of these is the Federal Bureau of Investigation's (FBI) Automated Fingerprint Identification System, with more than 630 million fingerprint images.

FACIAL RECOGNITION.
Facial recognition systems vary according to the features they measure. Some look at the shadow patterns under a set lighting pattern, while others scan heat patterns or thermal images using an infrared camera that illuminates the eyes and cheekbones. These systems are powerful enough to scope out the minutest differences in facial patterns, even between identical twins. The hardware for facial recognition systems is relatively inexpensive, and is increasingly installed in computer monitors.

EYE SCANS.
There are two main features of the eye that are targeted by biometric systems: the retina and the iris. Each contains more points of identification than a fingerprint. Retina scanners trace the pattern of blood cells behind the retina by quickly flashing an infrared light into the eye. Iris scanners create a unique biological bar code by scanning the eye's distinctive color patterns. Eye scans tend to occupy less space in a computer and thus operate relatively quickly, although some users are squeamish about having beams of light shot into their eyes.

VOICE VERIFICATION.
Although voices can sound similar and can be consciously altered, the topography of the mouth, teeth, and vocal cords produces distinct pitch, cadence, tone, and dynamics that give away would-be impersonators. Widely used in phone-based identification systems, voice-verification biometrics also is used with personal computers.

HAND GEOMETRY.
Hand-geometry biometric systems take two infrared photographs—one from the side and one from above—of an individual's hand. These images measure up to 90 different characteristics, such as height, width, thickness, finger shape, and joint positions and compare them with stored data.

KEYSTROKE DYNAMICS.
A biometric system that is tailor-made for personal computers, keystroke-dynamic biometrics measures unique patterns in the way an individual uses a keyboard—such as speed, force, the variation of force on different parts of the keyboard, and multiple-key functions—and exploits them as a means of identification.

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