photobomb

US /ˈfoʊtoʊbɑːm/
UK /ˈfoʊtoʊbɑːm/
"photobomb" picture
1.

to spoil a photograph of (a person or thing) by unexpectedly appearing in the camera's field of view as the picture is taken

:
•
My brother always tries to photobomb our family pictures.
•
A random stranger managed to photobomb their wedding picture.
:
gatecrashintrudebarge in
1.

an instance of photobombing

:
•
That was a classic photobomb by the dog.
•
We laughed at the unexpected photobomb in our group photo.