Why do people point to others in photos?

[2dp4u]

Hi PF, I have a question that I was wondering if you could answer; why do people point to the person next to them in photos? I saw some psychologist break it down a year or two ago and I can't for the life of me remember what he/she said. Shown below is an example of it and I've found it even more common when the people being photographed are drinking/drunk. They'll always point to them but sometimes they won't be looking at them (like in this pic), instead at the camera.
Thanks in advance!

[S. Earl Martin]

People react out of character when they are nervous or on the spot so to speak. They do all kind of stupid things when they are being photographed. The classic horns behind the head. People in the back ground dropping their pants. I once saw a photo where a girl grabbed a guy in the crotch she didn't even know, just as the photo was being taken. Drunk people act crazy anyway. It is part of being drunk. It lowers your inhabitions. This is why people take more risks and are more prone to fighting. Why people do this thing specifically? Who knows. Just trying to be funny probably. Or it is monkey see monkey do. They saw someone else doing it and they did it. Like a yawn it is contagious.