What is "rotoscoping"

vb. (present participle of rotoscope English)

Rotoscoping is an animation technique in which animators trace over footage, frame by frame, for use in live-action and animated movies. Originally, recorded live-action movie images were projected onto a frosted glass panel and re-drawn by an animator. This projection equipment is referred to as a rotoscope. Although this device was eventually replaced by computers, the process is still referred to as rotoscoping.

In the visual effects industry, the term rotoscoping refers to the technique of manually creating a matte for an element on a live-action plate so it may be composited over another background.