“Body double” is a catch-all term that might refer to a stand-in for an actor or celebrity, a photographic double or -- wrongly -- to a stunt double. The basic requirements of being a body double are living in Los Angeles or New York; having some acting ability; and, of course, having a physical resemblance to a particular actor. It’s also a good idea to be a member of the Screen Actors Guild.
Become a Background Actor
The basic route to being a body double is working as an extra, or background actor. Even actors who are doubles for well-known celebrities are referred to as "background" by SAG. To land this role, sign up with an agency such as Central Casting, a background actors casting company that lets you register online. Agencies want to place you in jobs because they get a cut of your pay.
Stand-Ins and Photographic Doubles
If you look a lot like a featured performer, you might get bumped up to stand-in, with a small increase in pay. In this job, you literally stand in for the actor while the crew lights the scene. If you really look a whole lot like a performer, the next rung is photographic double, where photographers shoot you from behind, or shoot part of you, as a substitute for the featured actor. Photographic doubles also substitute for actors in nude scenes, but they are still considered background actors.
Special Ability Doubles
There are several types of “special ability” background actors who also double for featured performers. These include everyone from golfers and tennis players to swimmers, skaters and musicians. For example, if the script calls for swimming but the featured performer has tattoos, or it would mess up the shot to have a left-handed golfer teeing off, or it's clear that the actor can't play the sax, the special-ability actor fills in for shots that don't show the actor's face. You go through a background casting agency for these roles, too.