Is there a way to search for an image in a group of them using a search engine, but not using keywords and instead using an actual picture? As a favor for a friend, I'm trying to see if she's getting BSed by her ex.

http://www.tasi.ac.uk/advice/using/finding.html

Interesting question,this link isn't quite what you want but it goes into the matter.
I'm gonna watch this thread...

I red a while back that google is now developing image search with pictures. but its not there yet.