EXIF Data

[Andrasta]

While most people have EXIF viewers in order to see the settings on photographs to adjust the same settings on the camera to improve photographs and possibly eliminate anomolies that appear. But, EXIF viewers also allow you to determine whether or not a photograph has been manipulated in any way from the time it was downloaded from the camera or memory card to the time it's presented anywhere online.

One can be downloaded here. I'm sure there are others around.