Image: NASA/JPL/University of Arizona
This began as an image of two craters on Mars, taken by the HiRISE spacecraft. I twiddled with the Polar Coordinates filter on my GIMP 2.6 to produce this. Happily, any HiRISE images from their website are in the public domain with no restrictions.
They have lots of cool pictures. Their webby place is http://www.uahirise.org/
|exposure mode||full manual|