Photobomb
The word photobomb originated in a 2008 entry on Urban Dictionary. The word is used to describe the moment when someone purposefully inserts themselves into a photograph when it’s being taken.
Source: twistedsifter.com
It’s generally done on purpose a prank, intending to ruin the shot. But photobombing has also become involuntary. We’ve all seen photos in which someone obliviously ruined the shot. Intentional or not, photobombing is a fun spin on photo-taking.