[nye2k]

Disney has used live action as a tool from early on, you can see this plain as day in Snow White's dancing scenes from 1937 because the movement feel awkward. And this is from animators with classical training who knew where the line needed to land on every frame.

Rotoscoping, tracing back each frame, is more what you will find in A-Ha's Take On Me music video, or Ralph Bakshi's film Fire and Ice. It is limited with poor line quality, and used primarily because the labor is cheap.