Understanding The Biometric Basis For Facial Imaging Biometrics

Facial-imaging biometrics are based, as you might think, on comparing information
from two digital images of faces to see whether they match. The problem is
that faces offer all sorts of challenges when you try to make direct comparisons,
so you should note the careful language in the previous sentence — “information
from two digital images” is not the same as “two digital images.”

For a good example of why we can’t just take two pictures and see whether
they’re identical, take a look at the angelic picture your sibling sent you of
your four-year-old nephew. Now, hold that picture up and suggest to your
nephew that he make the most horrible scary face he can, without using his
hands or artificial fangs. (As a side project, take a picture of this new face and
send it back to your sibling, titled “Reality.”) Do you think that these two pictures
would indicate these are even the same species when compared
directly to each other? Typical changes to facial appearance that would
throw off direct image comparison include (but are likely not limited to)

 Addition or removal of facial hair
 Body piercing
 Change in hair style
 Makeup
 Lighting changes from original image
 Different angle from original image

 Expression

 Tanning, black eyes, general pigmentation changes

Because it’s really not possible to rely on directly comparing the images pixel
by pixel, scientists have spent quite a lot of time figuring out how to represent
the essential information in a face mathematically so that they can correct
for cosmetic and imaging differences. The math is fairly intricate and not
appropriate for this book, but we include a short description of the principles
involved for the three main methods used in facial recognition.