The vehicle is called Opportunity, and was launched by NASA on what was supposed to be a 90-day mission to Mars in 2003, alongside its twin brother Spirit. Seven years on, long before Opportunity was supposed to break down and disappear from existence, the vehicle still leaves tire tracks on the Red Planet. (The Spirit, on the other hand, is missing in action, with the last communication received from the rover arriving in March 2010; no plans for a search and rescue mission are in place, of course).
The photo made public by NASA shows the tire tracks the rover leaves while going backwards during the 2,554th Martian day (or on April 1, for the Earthlings). NASA explains the bulges in the dust as being the result of a new technique for Opportunity to autonomously check for hazards in its way while driving backwards.
NASA is currently working on a new-generation Mars rover, with the first vehicle, the Curiosity, being in an advanced state of development. The new rover will be launched in between November 25 and December 18, 2011, as part of an unmanned mission.