Page 77 - Automated Fingerprint Identification Systems (AFIS)

62 AUTOMATED FINGERPRINT IDENTIFICATION SYSTEMS

the surface. Environmental factors such as heat and humidity also influence
how long the latent print will remain.
Latent prints are left by everyone on almost every kind of surface. Virtually
anytime an object is touched by the body, it retains some of the body’s sweat.
In the case of finger and palm images, these can form a unique combination
of ridges, ridge endings, bifurcations, core and delta locations, and other image
characteristics.
For a simple exhibit of a latent print, take a clear, colorless glass and wipe
the exterior surface to remove any foreign material. Put some water into the
glass. Next, hold the glass of water and take a drink. Put the glass down and
release it from your hand. Look at the glass. The images that you see on the
glass are latent prints.
Fingerprints have been compared to topographical maps. The contour lines
of the maps are similar to the friction ridges of fingerprints, which consist of
ridge endings, bifurcations, and dots. They generate a flow that can be identi-
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fied as a pattern. They do not appreciably change over time. Unlike contour
lines, however, friction ridges remain relatively uniform in their spatial dis-
tances and are rarely featureless. In contrast, the contour lines on a topo-
graphical map appear more closely together to indicate a sharp change in
elevation, and relatively large spaces between lines indicate that the surface has
only a gradual slope.
The finger image shown in Figure 3.4 is representative of the millions of fin-
gerprint images on file. The image contains a great amount of information that
contributes to the uniqueness of the fingerprint image, particularly to someone
trained to look for it. For example, the friction ridges flow around a center
area. If this were a topographical map, it would be interpreted as a mountain
or hill. The point at which the ridges form would be the top of that hill. The
change in elevation is constant and the ridges are uniformly distant from each
other. The white areas are creases or scars. The introduction of scars does not
negate the value of the fingerprint image. In some instances, it might even aid
in the identification, depending on the size and location of the scar.

3.5.2 PROVEN UNIQUENESS?
Can it be proved that no two finger images are the same? To do that would
require that every fingerprint be collected and compared. Each of the more
than six billion persons on this planet, most of whom have ten fingers, would

5 The fingerprint may slightly expand or contract with age and weight, or may become scarred.