From the NYT:
Dr. Farid and Eric Kee, a Ph.D. student in computer science at Dartmouth, are proposing a software tool for measuring how much fashion and beauty photos have been altered, a 1-to-5 scale that distinguishes the infinitesimal from the fantastic. Their research is being published this week in a scholarly journal, The Proceedings of the National Academy of Sciences.
here's one example of the before/after, more at the lab's website here.
Pretty impressive what can be done with a picture these days.
Kee and Farid, 2011, A perceptual metric for photo retouching is Open Access at PNAS