The technique of recording onto a screen and adding a background is commonly referred to as color keying, color-separation overlay, blue screening and green screening.
The most common colors used behind the footage to be projected are blue and green. These colors work well as they differ drastically from skin and eye tones, and are easily picked up by computer equipment.
The green screen was first developed by RKO Radio Pictures in the 1930s and first used in "The Thief of Baghdad" in 1940.
The background added to green-screen footage can be actual footage shot on location without the actors or a computer-animated scene.
When filming in front of a green screen, do not wear the color of the screen. If an actress wears a green skirt in front of a green screen, the green skirt will disappear from the final image.
Green screens have been used in various movies, including "Spiderman," "ET: Extra Terrestrial," "Star Wars" and "Back to the Future." Green screens are typically used in news channel weather reports; the weather reporter stands in front of a green screen while delivering the news and the map or weather background is added.