Image pixels turn into particles, and each follows some computed trajectory to effectively morph one image into another. I saw a similar effect in a movie and decided to try writing a program to do this. (I believe the movie was Antitrust, where artwork in the home of "Gary Winston" would morph between different images depending on who was present in the room).
Sample movie: [640x480 (10 MB)] or lower quality [320x240 (3 MB)].
Implemented painterly rendering technique described in J. Meier's "Painterly Rendering for Animation" (SIGGRAPH 1996) as my CS488 (Waterloo's Intro to Computer Graphics) project.
My ray tracer included support for depth of field, soft shadows, basic photon/illumination mapping, and a scene description file that used mathematical expressions for animatable parameters.