This story is nothing new, but although NASA and the NSA have strongly denied retouching any of their images, there are still plenty of people who believe!

The following movie is interesting, but unfortunately there is still no real evidence, such as before and after pictures that would support such clams. Perhaps one day someone will smuggle out some proof?

External links:
NASA Airbrushed UFOs / Lunar Base Towers (Google Video)
NASA home page