Databending
A nice way to waste time on a Friday afternoon is by databending jpg files. Open any jpg picture in a hex editor and mess around. Usually, you'll change the picture in glitchy, unintended ways. Sometimes, you get something interesting. Once in a while, the jpg is corrupted beyond repair, so make sure you're working on a copy. stAllio! has a decent and simple primer, and there is a databending photopool on Flickr. stAllio!, bless his heart, also has a primer on editing an image file in a wav editor designed for music (like Audacity). Here's a couple of original images and databends:
