I saw @zep's tweetcart and wanted to fiddle with it to produce something like the pattern on the bag he showed in the thread. I use Voronoi cells to apply multiple patterns to each image.
Unfortunately, with the limited resolution, our eyes can't pick out patterns unless they are at least half the size of the screen and very regular, so I had to use a limited number of cells with a reduced amount of randomness in each pattern. It sorta works, but it'd be way more effective on a hi-res screen with more cells.