Rotoscoping is the process of drawing animation over live-action film. This process was invented by the animator Max Fleischer for his cartoon animation series Out of the Inkwell in 1915. With the help of his brother Dave, Max illustrated the character Koko the Clown by having Dave dress up as a clown for reference. In 1917, Fleischer patented the process.
Studios had used rotoscoping for some animation movies such as in order to create realistic movements for otherwise stylized characters. The process was to film scenes with real actors and sets. Then, these images were used as references for the Disney animators to help them visualize the scenes, postures and movements to draw.