Even if the Mars Rover sent a clear photo of a Martian shaking his fist at the camera, NASA would never acknowledge it or release it to the public. NASA is a government agency which, like all government agencies, must continually take care to manage public opinion with half-truths, distortions, lies, and lots of those air-brushed photos and computer-generated images! 

http://thelede.blogs.nytimes.com/2012/12/03/mars-rover-discovery-revealed/