I've seen this done with great success on another forum, fun for everyone involved. You simply take the image that was posted by the previous poster and edit it with Photoshop or a similar program. No limits or rules on how you edit it except that you keep it safe for work. Then the next person takes it and edits it again, and again, and again. The image, as it goes through it's progressive edits, eventually becomes downright unrecognizable, and ridiculously amusing. Here's the image, a simple stock photo.