One of the nice many bits included in Pixlr for free is the extensive adjustment and filter system that can be applied to images.  You can easily make something black and white, posterize, add scan lines, and do all sorts of other global changes to an image or single layer.

Objective: Change an image by using Pixlr's adjustments or filters (or both).

Directions:

1. Go to http://pixlr.com/ and select the Pixlr Editor
2. Upload your image or open one from a URL
3. Apply filters and adjustments to your image (to your liking)
4. Repeat this until you have three different "looks" for the same image
5. Post all three in the discussion board