A body double is a general term for someone who substitutes for the credited actor of a character in any recorded visual medium, whether videotape or film. The term is most commonly used in the context of head-to-toe (or nearly) shots involving nudity. For example, Catherine Bell served as a nude body double for Isabella Rossellini in the movie Death Becomes Her. More specific terms are often used in special cases; a stunt double is used for dangerous or sophisticated sequences. This is in contrast to a stand-in who replaces an actor for non-filming purposes such as scene arrangement and lighting adjustments.
Stunt double and body double can both be used for cases where special skills are needed—anything from playing the piano, to competitive skiing.
Also, if only a part of the body is shown, the term might be more specific; probably the most common is a butt double, mostly used with TV, since whole-body nudity isn't as common in that medium. The term stunt butt is also attested.
A production scene photo double portrays a double of the lead "star" actor for the director. A double will be seen on camera during the movie. Some of these many "double" acted scenes could be long or wide 'establishing' shots, complicated 'over-the-shoulder' main lead actor's dialogue sequences or in quick 'insert' close-up shots involving only showing actor's body parts.
The photo double must say the dialogue lines in the same lead actor timing and also reproduce the exact physical actions "blocking" in co-ordination with the other principle "star" actors in that scene to make this scene 'real' since it will be seen in the final cut. This is important to establish since the public thinks there is very little "acting" talent to this important production job.
Usually the "double's" face is kept from being seen on camera. This way the "star" can work in fewer scenes and the "star" lead actor can be literally filming in two scenes at once. And in this way, a good cast photo double can help speed up the day's production and is a necessary and valuable cast person for a film.
The 1984 film Body Double, directed by Brian De Palma, featured a plot that hinged on the discovery that one character had in fact served as a body double for another; whether the nude scenes in question were actually done by either of the two actresses or by an unaccredited body double is unclear.