I didn't know what "Error Level Analysis" was. So: 'Error level analysis (ELA) works by intentionally resaving the image at a known error rate, such as 95%, a

I didn't know what "Error Level Analysis" was. So: 'Error level analysis (ELA) works by intentionally resaving the image at a known error rate, such as 95%, and then computing the difference between the images. If there is virtually no change, then the cell has reached its local minima for error at that quality level. However, if there is a large amount of change, then the pixels are not at their local minima and are effectively “original”.' From http://www.hackerfactor.com/papers/bh-usa-07-krawetz-wp.pdf http://www.hackerfactor.com/papers/bh-usa-07-krawetz-wp.pdf, a lot of interesting stuff in there.