Rotoscoping

Rotoscoping is an animation technique invented by Max Fleischer in which live-action figures are cut out and re-drawn. This has historically been a valuable invention because animated figure movement could be much more realistic using a rotoscope (the actual instrument used). The Fleischer brothers used this technique to animate Koko the Clown.

The technique was later used by animator Ralph Bakshi for his animated adaptation of J.R.R Tolkien's The Lord of the Rings. Richard Linklater used a version of the technique for his films Waking Life and A Scanner Darkly.

Rotoshop
Rotoshop is a computer program used to animated live action frame-by-frame and can be seen in the two Richard Linklater films listed above. Rotoshop can "interpolate between brushstrokes to save time and smooth motion" (link).