The definition of animation has become problematic with the advent of digital media. The informational character of digital moving images has made it difficult to distinguish between what is animated and what is a reproduction of recorded movement. Previous definitions of animation, as a non-recorded (non-live action) illusion of motion and as a frame-by-frame production, do not encompass the automation of many digital illusions of motion, nor do they describe the way in which some digital moving images derive from records of movement. In this light, this article contends that animation can be distinguished in digital media by virtue of traits specific to its solely illusory motion and that are general to all animation production techniques, whether analogue or digital. The article develops a set of criteria to emphasize animation’s illusion of motion; it also examines which aspects are shared with other moving images and which are exclusive to animation. Additionally, the author deals with the persistence of the index in digital media and the authorship of automatic animations.