Copymove by John Graham-Cunning detects image manipulations which have been created with the clone tool.

NEW: GIMP plugin added. Compile and install with:
$ CC=g++ CFLAGS=-O3 LIBS=-lpthread gimptool-2.0 --install elsamuko-copy-move.c
You will find the plugin then under Image->Copy Move.

NEW2: W32 version added.
NEW3: Standalone version using Qt with QThreads.

Update1: Linux version with multithreading and can be used for bigger images now.
Update2: Massive speed gain thanks to the hint of Luca Del Tongo:
http://blogs.ugidotnet.org/wetblog/
The calculation only uses the lower frequencies of the DCT now.


Original (cc from Mark Hogan):

Cloned out sign:

 $ ./copymove warning_clone.jpg  2 10

Result: Manipulation detected :D

More information:
http://lemonodor.com/archives/2008/02/protecting_journalistic_integrity_algorithmically.html
http://www.jgc.org/blog/2008/02/tonight-im-going-to-write-myself-aston.html
http://www.ws.binghamton.edu/fridrich/Research/copymove.pdf
Y. Huang, et al., Improved DCT-based detection of copy-move forgery in images, Forensic Sci. Int.
(2010), doi:10.1016/j.forsciint.2010.08.001