http://homepage.mac.com/gapodaca/digital/digital.html

This impressive page allows users to scroll the mouse over touched-up photographs and see the original. Some of the differences are startling. We and our students know that airbrushing and other digital magics make some pictures (especially of famous persons) more appealing. But I think these are some good examples of how drastic that can be.

http://www.pbs.org/ktca/americanphotography/features/art.html

This PBS site on photography throughout the century also has an interactive Image Lab that's worth checking out.

http://www.cs.dartmouth.edu/farid/research/digitaltampering/

This is a great collection of digitally altered pictures.