[gtfierro]

If you look at the "image" description files (e.g. http://essenmitsosse.de/pixel/scripts/zeus.px, linked by another comment), then it looks like the files define a set of constraints on the "components" in an image such as Zeus's arm , the bird beak, the cow's leg, etc. When the mouse moves, my guess is those constraints determine which components are rendered and where they appear on screen.