Understanding The Biometric Basis For Fingerprints

An image of the pattern of ridges and furrows that cover our hands, feet, and fingers can be optically captured at a point in time when we’re certain of the identity of the provider, and then later compared to a new image to authenticate that user. Although fingerprints change size as we grow, the structure of the ridges and furrows doesn’t change at all over time, except for essentially mechanical alterations such as cuts or scars.

We use our hands a lot, so the possibility that our prints become marred by
damage, temporary or otherwise, is much greater than that of damage to,
say, our eyes or facial structure. Physical damage to your fingertip means it
doesn’t look the same as when you captured your print for identification —
and the system may reject your identification if it can’t exactly match one or
more of the unique characteristics.

Although — in theory, anyway — we could use any portion of our feet and
hands that have identifying characteristics, in practice the tips of each finger
or thumb are the easiest to position for imaging. They’re so easy, in fact, that
each of us leaves perfectly legible copies of our fingerprints on objects we
touch all the time — as many criminals have learned the hard way. While this
makes finger- and handprints very convenient as a biometric identification, it
also makes finger- and handprints among the best-documented (and most
generally available) biometric identifiers we have.

Fingerprint, and by extension palm-print, readers come in essentially three
forms:

Optical: These work much like a regular image scanner, where a light
source is used to illuminate the surface of the scanner area and a chargecoupled
device array collects an image of the illuminated surface.

Thermoelectric: Thermoelectric scanners use substances that electrical
properties are influenced by localized heat sources (like your finger) and
read the electrical variances in the surface to acquire an image of the
fingerprint.

Ultrasound: Ultrasound imaging of fingerprints bounces very high
frequency sound waves off the three-dimensional structures of your
fingerprint and records the 3D model acquired.