The shadows are definitely caused by UFO's ;-) (note to Mod Bob: don't take this too seriously, it's just imagination.)

Note to ER: When I posted the words: "Is it unreasonable to assume that the laws of physics may have allowed life on Mars." I was thinking that pretty well all of the minerals that exist on Earth have also been detected on Mars, the only difference is in the quantities compared to each other, for instance the atmosphere on Mars has more carbon dioxide and less oxygen than the atmosphere on Earth. There are other differences that are known to anyone that is even mildly interested in knowing something about Mars. Such as; Mars is smaller, it is further from the sun, it has less atmosphere, it has less water, etc., but what was going through my mind was: Do these variations definitively exclude the existence of life on the planet.

I figure that if we knew how life started on Earth and why it is spread so widely on Earth, then perhaps that knowledge could be used as a basis for extrapolation of the possible existence of life on Mars.

As for the observed "shadows," my personal hypothesis is that the camera that took the pictures was behind some type of a protective "glass" and the camera was panned in order to get the best match to the ground features.
If this was the case then the "shadows" could have been dirt on the protective panel and the apparent motion was due to the camera motion.

I have no idea what kind of system was used, but this explanation seems like one that could explain the "shadows."

Johannes