In cinematic special effects, there are two different types: practical and digital. Digital special effects are created through the use of computer programs and blue and green screens, whereas practical effects use real world elements such as plasters, make-up and prosthetics.
One of the earliest instances of special effects was used in a minute-long 1899 French movie called "The Conjurer." In it, famed French magician, Georges Melies, made himself and his assistant disappear by splicing together different shots. Advancements in computer programming have allowed techs to use methods like green screen technology to create impossible displays, such as ordinary men flying through the air.
Using a technique called chromakeying, or color keying, special effects artists are able to remove an entire shade of color to create a transparent portion, with green and blue being the most popularly used. In the case of green screen, the green backdrop is digitally removed during production to allow for a new image or images to be put in its place. The most common use of green screen special effects technology can be seen daily on your television during your local news. Weather forecasters stand in front of a screen that is filtered out to allow for an animated map of the country to be shown behind them.
Smaller scale use of chromakeying special effects include making an actor an amputee, as seen in "Forest Gump" with Gary Sinise's character, Lieutenant Dan. The actor is filmed with a solid color material wrapped around their limbs and, during production, that shade of color is completely removed from the shot. Post-production touch-up software allows for the effects artists to clean up the image to look real.