Page 80 - Automated Fingerprint Identification Systems (AFIS)

FINGERPRINTS ARE UNIQUE 65

quent coding and comparison. A good capture includes three levels of ridge
details: 6

• Level 1 detail includes the general ridge flow and pattern configuration.
Level 1 detail is not sufficient for individualization but can be used for exclu-
sion. It may include information enabling orientation, core and delta loca-
tion, and distinction of finger versus palm.
• Level 2 detail includes formations, defined as a ridge ending, bifurcation,
dot, or combinations thereof. The information of Level 2 detail enables
individualization.
• Level 3 detail includes all dimensional attributes of a ridge, such as ridge path
deviation, width, shape, pores, edge contour, incipient ridges, breaks, creases,
scars, and other permanent details.

The characteristics of an ideal image for an AFIS search are the same as in pre-
AFIS days. It should be a clear image, rolled from one nail edge to the other,
using even pressure that results in an image in which the ridge shapes, devia-
tions, and pore locations can be distinguished. The advantage with AFIS is that
features such as ridge endings, bifurcations, and ridge flows can be extracted
electronically by a coder in just a few seconds. These same features can be
extracted identically time after time.
AFIS systems can be used to search multiple fingers. For tenprint identifica-
tion purposes, this may be accomplished by using two fingers. In most instances,
the information from the patterns of all ten fingers and two finger images is
sufficient for identification. In addition to the images, other biographical infor-
mation, such as sex, may be used to reduce the need to search the entire data-
base. Using two fingers does more than just double the changes of making an
identification. Since each of the finger images is coded and is launched in a
separate search, the results should come back with the target as the first, and
perhaps, only candidate. The synergy of two fingers from the same individual
supports the opportunities for identification. If all finger images on file had
even clear level 2 detail this would certainly happen.
In tenprint processing, some AFIS systems use images of the two index
fingers and some use the two thumbs. There are at least two arguments for
using thumbs. The first is that the thumbs offer more surface area than the
index finger, producing a larger print image. The second argument is that if
the search on thumbs produces no identification, the record can be sent to the
Integrated Automated Fingerprint Identification System (IAFIS) or another

6 See Ed German’s remarks on this at http://onin.com/fp/level123.html.