rotoscoping

Max Fleischer

Rotoscoping describes the process of manually altering film footage one frame at a time. It was invented in 1915 by animator Max Fleischer to improve the movement of animated characters and make them look more realistic.

The technique was originally achieved by filming scenes in live action and then projecting the film onto glass panels so an animator could trace the action in every frame, thus capturing the movement of the actors. Adopted by Disney in the 1930s, many of their celebrated early titles like Snow White and the Seven Dwarves, Cinderella and Alice in Wonderland were all created via rotoscoping.

Great Examples from:

https://www.intofilm.org/films/filmlist/87