TinEye is one of those tools you dreamed about but were not available. Up to now.
Any photographer is concerned about the possibility of seeing his/her images taken from his/her web site and used elsewhere. Usually, it is impossible to find the copies, even if you know your images well. TinEye will find copies of your image/photo, even if it is squeezed, enlarged, cropped, with an added watermark, etc. It is even able to find near matches (photos that look a bit like yours and could be heavily modified copies or plagiarism).
You can ask it to use an uploaded JPG bitmap or direct it to the image on the web.
Check the “cool searches” they use as examples and then try with your own images. Of course, it does not have indexed all the Internet and (I am sorry to say it so bluntly) your photos may not have been deemed worth copying. But I tried it on several of my own photos and it is clear that it will find all kinds of borrowed photos on theweb.