The camera aboard Mars Global Surveyor weighs in at about 46 pounds, and are 34 inches long and 15 inches in diameter. In normal operational use, it is capable of imaging objects of up to 1.5 meters per pixel, meaning that you can pick out an object of 4-5 meters across. However, the camera operators have developed a technique of rolling the spacecraft along its flight path to "slow down" the camera in sync with the rotation of the planet, allowing it to effectively stay positioned over a target area longer. This boosts picture resolution of up to 0.5 meters per pixel, allowing objects as small as 1.5 meters to be seen on the surface of Mars about the size of an Mars Rover.
While distances and atmospheric conditions between Mars and Earth aren't quite the same, the basic technique can be used to effectively improve the imaging capacity of any satellite by a factor of three. India has quietly used the technique to squeeze better pictures out of their earth observation satellites, getting 1 to 2 meter resolution out of cameras designed to deliver 2-3 meter resolution in normal operation. The satellites essentially serve double-duty, monitoring the environment and crops for the civilian sector and providing more detailed imagery of Pakistan, China, and other potential conflict areas. Doug Mohney
Satellite photography techniques developed for use over Mars since 2004 have been quietly used for years by the U.S. military and other countries. The Mars Global Surveyor went into orbit around Mars in 1997 and has been snapping pictures of the planet ever since, including photographing the landing sites of the Viking landers, and the currently operational Spirit and Opportunity Mars Exploration Rovers (MERs).