I did some facial recognition work years ago using eigenfaces and some work by Joe Atick, author of the FaceIt facial recognition program.
in reply to Computer Vision Libraries
Human faces are special; we seem to have specialized areas in our brain devoted to face recognition and reading facial expressions. So, other than image registration and normalization, the usual CV techniques of edge dectection and image segmentation don't work so well here. In other words, generic computer vision libraries won't be so helpful.
If I wanted to solve this problem, I would first check out some of the open source
face recognition programs, find one I liked and then create a perl binding. One of the stronger programs out there is the CSU face recognition program It has a number of algorithms to compare and the C source is available.