I have my Win7 backgrounds setup for a slide show, so here's all the ones I currently use.The originals are sized to stretch across my two widescreen monitors. This is my work computer, so no icons.
BTW, the fourth one down looks like a render, but it is an actual photo of Mars from one of our spacecraft!
I believe that fourth one is a crop of the image which can be seen on this page
, and that the crater on the terminator just above the center in your image is Gale Crater, site of the recent Mars Curiosity rover landing.