Each person adds something to an image in MS Paint (you can use GIMP or Photoshop if you want, I suppose, though). After adding something, the person replies to the thread with the image.
Some Rules:
No removing what someone already added.
Only add one thing at a time.
Don't make something so big it covers a third of the image
You can make the work space larger.
Nothing inappropriate.

Ready?

A circle!