How to detect digital fakes?

Common logic
The logic is necessary to detect a fake photo, if something is utopia but it's in the photo probably had been modify.

Lighting
The light conditions is different from the original photograph because it depends on the place that the photo had been taken, and if you see over brightness in a photo its probably a fake picture.


Eyes and Positions
The eyes because eyes have very consistent shapes, and if someone edit a picture the eyes get distorted from the real one's and it's easy to find out the fake.

Specular HighlightsSurrounding lights reflect in eyes to form small white dots called specular highlights. The shape, color and location of these highlights tell us quite a bit about the lighting.

http://www.scientificamerican.com/article.cfm?id=5-ways-to-spot-a-fake&page=5