The term "photobomb" refers to the act of entering into someone else's photo at the last minute, altering the intended composition of the photo. Photobombing can occur in nearly any type of photograph, regardless of the subject.
Photobombing can be either intentional or unintentional. An intentional photobomb, as the name states, involves one or more parties entering into a photo that they are not a part of with the express intent of making themselves the new focus of the photograph. There are many popular images of celebrities photobombing each other at awards ceremonies and public events. In some cases, props or costumes are used in a photobomb to achieve a comedic effect.
Unintentional photobombs happen when someone accidentally wanders in front of or behind the intended subject of a photograph. This type of photobombing is common in crowded areas, such as amusement parks or shopping malls. Typically, the person performing the photobomb looks towards or faces the camera as the picture is being taken, transforming him from simply a face in the background to the new focus of the photo. Photos in which the photographer is facing the camera at himself, without the ability to see what is actually in the shot, are likely to suffer from unintentional photobombing because of the lack of compositional control.