I recently got an Android phone. One of the apps that I enjoy playing with on it is ‘Google Goggles’. You take a photo with the phone’s camera and then Google Goggles fires a search to get you more information about the thing you just clicked. It’s often eerily accurate.
Facebook allows your photos to be tagged by others. It’s only a matter of time that they plug in face recognition. iPhoto does it, Picassa does it, I see no reason why Facebook won’t (if it doesn’t already).
So you take a photo, use something like Google Goggles for Facebook, and voilá you have (depending on the user’s privacy settings) details of the person you clicked!
It isn’t called Facebook for nothing.