Can a chimp understand what a photograph is?

When a friend asked me this, my first thought was "no." I'd never read of it, and recognizing a photo requires some abstract thinking beyond what we usually ascribe to even the smartest nonhuman mammals.  Well, it looks like I was wrong.  Chimps have associated a photo with a human in studies that concluded "Results indicate that the chimpanzee is able to recognize individual humans from novel photographic representations." Other studies who chimps can recognize each other in photos. There is even IgNobel Prize-winning research (done in California - why does that not surprise me? ) that shows a chimp can recognize another chimp from a photo of its butt.  It can also tell the sex of another chimp from a butt photo.  I'm not sure what conclusions can be drawn from that. Maybe a chimp could tell me.