A stand-in is any person who is used to replace lead actors and stars for tedious parts of filmmaking. These are primarily camera and lighting tests, but can include to a lesser extent costume tests, temporary dialogue partners or as a replacement for close-ups hands, feet etc. Stand-ins do not show their face or have their voice in the final film.
A double is someone who is used in place of a cast member where the real actor cannot be used because of danger or other reasons. Doubles usually physically resemble the actor they are replacing (in body size, shape and clothing) and are often dressed in wigs to complete the illusion. Doubles are used for things such as dangerous stunts, sex scenes or scenes requiring nudity where the actor refuses to do it, situations where the same actor must appear to confront themselves and so on. One very clever use of a double was in the film The Crow. In order to complete the film after Brandon Lee’s accidental death on set, the filmmakers shot a couple of critical scenes using a body double (someone that looked like Brandon physically). In post-production the effects team digitally super-imposed Brandon’s face over that of the double. The effect worked seamlessly.
