-This takes an image, divides it into a grid, and then randomly shuffles
-the squares around as if it was one of those annoying "16-puzzle"
-games, where there is a grid of squares, one of which is missing.
-I hate trying to solve those puzzles, but watching one permute itself
-is more amusing.
+A variant on a "fifteen puzzle", operating on the screen or an image.
+It divides the image into a grid and randomly shuffles the squares.
+
+http://en.wikipedia.org/wiki/Fifteen_puzzle