you can't "biometrically" compare photos. The word biometric implies that some metric is being collected directly from the biological specimen. This is why locks that open by fingerprint are said to be biometric locks. It is possible to record things like facial structure positioning through images, though that's a little different. Doing that type of comparison requires specialized software that only people who work with computer vision algorithms (or general math/comp sci geeks like myself) would be familiar with, but I'll post a few links later on if I have time.