Page 78 - Automated Fingerprint Identification Systems (AFIS)

FINGERPRINTS ARE UNIQUE 63

Figure 3.4
Finger Image

have to be fingerprinted. Those prints would build a database of approximately
60 billion images, which would then have to be searched by the ten fingers of
each of the six billion people. In AFIS parlance, this is called a self-search, i.e.,
a portion of the database is searched against the rest of the database until the
entire database has been searched against itself.
There are instances in which a person has been fingerprinted more than
once and the identification is missed on a subsequent search, perhaps because
of a poor-quality set of images on the database, poor-quality inked impressions,
or inaccurate data entry. When these records are found, the images are
reviewed by a print examiner. If the different records are of the same individ-
ual, the records are consolidated into one record, usually the one with the ear-
liest state identification (SID) number. There are also instances in which an
identification is made on an individual whose finger images match the inquiry
card, but the name (or some other characteristic) does not match. What is the
true name of the subject? The identification agency can only report on the
information it has on file.
Large identification agencies may initiate a self-search of the database once
the system is fully operational or when major improvements to the system have
occurred, such as the installation of more accurate matchers (which house
extracted image characteristics) that will match minutiae with a higher level of
precision, or improvements to the coders (which extract features from finger
images) that will more accurately find the minutiae in the finger image. For
example, a few years ago a large state identification agency installed new coders
and new matchers, and systematically began to undertake a self-search. In
searching the two index fingers of these five million records, the agency uncov-
ered hundreds of records that had to be consolidated, some with more than
ten entries for the same person. In all of those searches, however, there was not
one instance in which two different persons had identical finger images. Five