How to discover an image clone I have an image depicting a results of gel electrophoresis (it does not really matter - it just means: no bodies, faces, predictible objects) and I have a strong suspicion that a part of the image background was copied (probably Photoshop Clone Stamp) to cover an unwanted peak. The background is really just noise, but it should be almost perfect copy. I am not entirely sure how big is the copied area so just straightforward cross-correlation with an image part won't work.

How do I prove that? I prefer Matlab for such tasks.
Maybe this is an appropriate paper for you: Exposing Digital Forgeries in Scientific Images, by Hany Farid (freely available, e.g. at http://www.ists.dartmouth.edu/library/199.pdf).