With a new child, people are always asking if the baby looks like the father or the mother – probably a prehistoric social reflex to confirm that this is your offspring that you are caring about.
Face recognition clearly is a science of its own – a lot of heuristics and Bayesian computing – more at face-rec.org – and even a big business if you think of automatic passport control or age determination for goods that are only allowed for adults.
Face recognition works quite robust as I found in the advanced online demo at betaface.com. A new browser plugin from polar rose will even allows to annotate web pictures – Orwell meets Flickr.