Sri Lankan site Groundviews uses Twitter to contact former UN spokesperson Gordon Weiss about photos that showed proof of government slaughtering of civilians during fights with the Tamil Tigers. After obtaining the photos, they opened them in Photoshop and checked the timestamp. The timestamp, which is a code placed in each photo file in by a camera to show when the photo was taken, did not correlate with the time of events in the report.
Through some simple investigation by this citizen outfit, it was found that these photos were problematic in being used to prove war crimes. Groundviews pointed out that the government and pro-government media would pick up on this as proof that allegations about war crimes are false.
Lesson: even if you have photographic proof, some simple gaps in fact checking will undermine all of your work.
WARNING: Graphic photos at the following link.