Today's Image of Mars was taken by HiRISE to determine if there was a crater present on the dune. As of 2011 scientists have yet to find a dune with a crater on Mars. This leads them to believe that dunes are recently developed features, since older features generally have craters.
This particular dune was imaged in the southern hemisphere during late fall, so frost has begun to accumulate. To better see this you should check out the high resolution version of this image. Clicking on this image will take you to the caption from HiRISE.