I'm often surprised by the human ability to correctly identify other individuals despite significant modifications due to ageing, hairstyle, injury, etc. But, sometimes the addition of a beard and a hat can radically increase the identification error.
I wonder whether all facial regions are equally important when we try to recognise human faces? Do we focus more on some regions than others? I doubt that this is the case, but I'm not certain.
Update:
So far I've read through the following:
1) http://en.wikipedia.org/wiki/Face_perception
2) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2998394/
So far I haven't found an answer so I decided to try Biology.StackExchange.