Huh, what? You say. Well, as the title states, it is REVERSE, meaning you put in a picture instead of text, and it searches..... well, you know.
Anyway, I happen to find a site that sounds interesting... although, you could probably google this topic's title.
http://www.halfbakery.com/idea/Reverse_20Google_20Image_20Search
If you happen to find anything to do with Reverse Image Searching, post here.
TinEye (http://www.tineye.com/) is the only working one I'm aware of.