PES: I worked on this for years!
Every year, it gets more and more difficult to draw a clear boundary between animated and live-action films. The official terminology used by the Academy Awards feels particularly vague and anachronistic:
An animated film is created by using a frame-by-frame technique, and usually falls into one of the two general fields of animation: character or abstract. Some of the techniques of animating films include cel animation, computer animation, stop-motion, clay animation, pixilation, cutouts, pins, camera multiple pass imagery, kaleidoscopic effects, and drawing on the film frame itself.
This definition feels like a half-step up from we know an animated film when we see one. When you get down to it, don't all movies use a frame-by-frame technique? The fact is that nowadays, all of the boundaries are blurring – even within the world of animation. Stop-motion animation is not necessarily a separate species from computer animation.