A professor of computer science and digital forensics expert, Dr. Hany Farid has became interested in this problem. Him and Eric Kee a Ph.D. student in computer science mad a proposal of a software tool for measuring how much fashion and beauty photos have been "photoshopped" ranking on the scale from 1 to 5.
The algorithm behind the tool ca supposedly can human perceptions, therefore an online community of couple of hundred people was asked to compare before and after images then classify them from 1 to 5, one being minimally altered and five for severe case of retouching the original image.