This December 2006 news article suggests that 'about a dozen' spacecraft on Mars have been seen from the MRO which is interesting. What is be even more interesting is that the scientists can obviously identify individual rocks seen with the rover's pictures of a metre or more in size taken at the landing sites.
It's like finding a needle in a haystack what NASA's Mars Reconnaissance Orbiter (MRO) has done. It has spotted about a dozen US landing spacecraft on the Martian surface and, incredibly, taken pictures of such accuracy that scientists have been able to identify individual rocks that were first photographed by the Viking landers in 1976.
The Spirit rover, which landed in 2004, as well as both Viking landers can be seen in the new images. The pictures show both of the Viking landers as well as their nearby heat shields and backshells. These are the top and bottom covers of the capsules in which the rovers descended through the Martian atmosphere.
It is strange that we get such bad photographs of the disintegrating Phoenix.
Due to the URL, I assume this picture of Spirit from above was taken in 2004 and although I personally have not reached this conclusion, it may lend credence to the theory that some, if not all Rover pictures are taken from space.