It's a little-known fact that Disney Studios has been using rotoscoping since "Snow White". 

Rotoscoping was invented in the late nineteen-twenties by his rivals, Max and Dave Fleischer, for their silent "Out of the Inkwell" cartoons featuring Koko the Clown. The technique was quite advanced by the early thirties. When Disney started working on feature-length cartoons, it was important to animate humans in such a way that they could carry a story dramatically. Disney's animators shot reference film in live-action, using actors (often the ones who provided the characters' voices), for virtually every "human" character, and quite a few non-human ones as well. Much of this reference film still exists in the Disney vaults today.

The studio never called it "rotoscoping" becuse they didn't just trace over the film exactly, the way the Fleichers had. They exaggerated certain movements to give charcaters more of a "cartoony" feeling. So they always referred to it instead as reference film.

But, yeah, Disney animators have been rotoscoping since the very first full-length feature ever animated.

-jjsemp