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How it works
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Score
– A number indicating the degree of similarity or correlation of a
biometric match. Traditional verification methods – passwords, PINs,
keys, and tokens - are binary, offering only a strict yes/no
response. This is not the case with most biometric systems. Nearly
all biometric systems are based on matching algorithms that generate
a score subsequent to a match attempt. This score represents the
degree of correlation between the match template and the reference
template. There is no standard scale used for biometric scoring: for
some vendors a scale of 1-100 might be used, others might use a
scale of –1 to 1; some vendors may use a logarithmic scale and
others a linear scale. Regardless of the scale employed, this
verification score is compared to the system’s threshold to
determine how successful a verification attempt has been.
Incidentally, many systems return a score during enrollment,
referred to as an enrollment score or quality score. This score
refers to how successful the extraction process was at finding
distinctive features in the biometric sample. If the sample was rich
in information, there will likely be a high enrollment score. This
score is not used in the matching process, but might be used to
determine whether a user can enroll successfully. A low quality
score may indicate that the user cannot be reliable verified.
Threshold - A predefined number, often controlled by a biometric
system administrator, which establishes the degree of correlation
necessary for a comparison to be deemed a match. If the score
resulting from template comparison exceeds the threshold, the
templates are a “match” (though the templates themselves are not
identical).
When a biometric system is set to low security, the threshold for a
successful match is more forgiving than when a system is set to high
security.
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