Image editing is not something new. The Soviet Union did this back in the 1920's and 1930's, famously editing people out of photos who had become enemies of the government.
This has been made a lot easier nowadays with the invention of tools like Photoshop, and has been used in a lot of situations. For example, Time Magazine darkened a picture of O.J. Simpson in 1994, which Newsweek ran without changes. Many people felt that Time Magazine's portrayal was in poor taste, if not racist.
In a more amusing twist, the Buffalo Bills recently fired their head coach, Dick Jauron. They gave out team photos to fans at a recent game, and edited the former coach out, even as they left players there who had been cut from the team. Viewing the high-resolution version of the picture, you can see a lot of things that aren't quite right, for example, look at the size of #31 Jairus Byrd's right arm. There is a complete discussion of this on a Bills message board, and this also appeared on ESPN's Web site.
From Trotsy to O.J. to Jauron, image editing has many forms, and you can see why a simple photograph isn't evidence enough nowadays.