Maybe with an optical mouse for an eye, generate a “decision” from the image of the paper fibers and paint under the “head” of the line follower that would select the next direction and color to put down (or change in direction and color). Maybe stack a few standard image processing algorithms to come up with the “decision”. Might end up with some interesting, organic looking, artwork.
Maybe even have the rules of the “decision” change based on the image underneath. Seeing enough blue could trigger some color and some sharp direction change.
Probably wouldn’t be too interesting on a small canvas, but something like a mural might be.
Maybe have the color influenced by absolute position so things like logos or big faces could be subtly hidden in.