I spent an hour or two last week re-implementing the Mozilla "hack" artwork. The original art appeared on t-shirts and stickers. Now you can have it on your desktop.
The artwork was originally implemented by BLK/MRKT, Shepard Fairey's previous design firm. The red t-rex, the star, and the "revolution" font make for a compelling call to action and communicate as effectively as I can imagine our shared responsibility as put forth in the Mozilla Manifesto

I've tried to cover the most popular desktop sizes, and a range of 4:3 and 16:9 sizes should be scalable to whatever you're using. But, if I've missed a scale you really want, please let me know.