This article is from the Conspiracy Theory Literature FAQ, by Xavier Poez firstname.lastname@example.org with numerous contributions by others.
A major CTL theme advanced by Richard Hoagland is that NASA knows
about the existence of aliens and/or alien artifacts on different
planets, but suppresses the information. Supposedly there are teams
that airbrush photos or review them for unauthorized detail prior to
releasing them, and secretly stockpiling photographs that reveal
anomalies. Some CTL claims NASA was involved in faking the entire
Apollo moon landings. See [Brian].