Size Constancy

The perceptions of the size of objects is constant even though the size of the object on the retina varies with distance.
Everyone in the left photograph seems to be the same size right?

Take a look at the photograph on the right. The man in the white shirt was copied and pasted next to the woman on the left to show how the size varies with distance.

http://psych.hanover.edu/Krantz/sizeconstancy/page2.html