This site has a GIMP script for doing Error Level Analysis: http://sites.google.com/site/elsamuko/forensics/ela http://sites.google.com/site/elsamuko/forensics/

This site has a GIMP script for doing Error Level Analysis: http://sites.google.com/site/elsamuko/forensics/ela http://sites.google.com/site/elsamuko/forensics/ela (After saving it to your ~/.gimp-2.6/scripts folder, the tool hides in the Image menu.) I just tried it on a couple of my own images, the results are very interesting.