HAS A PHOTO been severely altered? I’m sure you’ve seen examples of photo forgery lately in the news media. How exactly can you detect if a photograph is a composite of more than one original camera image? How can you tell if the clone tool has been used on an image, replacing scene detail at one part from another?
See the Digital Forensics webpage for original research by Hany Farid and his group at Dartmouth College.
Of particular interest is a large PDF file of lecture notes, which starts out with a number of famed doctored photographs from history, and then immediately jumps into complex mathematical examinations of digital images.