photobombverb [ I or T ]
uk/ˈfəʊ.təʊ.bɒm//ˈfoʊ.t̬oʊ.bɑːm/informalto appear behind or in front of someone when their photograph is being taken, usually doing something silly as a joke:
We were photobombed by a guy dressed in a gorilla suit.
photobombing
noun [ U ] /-ɪŋ/
Even celebrities have joined in the craze for photobombing.