This is a scaled down version of the image at http://ltpwww.gsfc.nasa.gov/tharsis/ngs.html. That image is 1280x782 pixels, which doesn't fit on a 1024x768 pixel monitor. This page serves the same jpeg file, but scales it down to 960x576. It's still worth visiting the Nasa page. The full-scale image has more detail and they have some text explaining how it was made.