bluecatconsidering it a photo of a rock face from a few metres away, the rectangle would be maybe an inch in size.
Size does not matter in an alien world. We have found plenty of small items which were out-of-place in an uninhabited world and many people believe there is no limit to the diversness of life throughout the universe. Big, small, carbon based, non-carbon based it really does not matter when the home environment is very different from our own and the species has had billions of years to develop.
Good question. Maybe this is just a product of the Gigapan stitching process and not real. But if that were the case why isnt the mastcam right pic in the archive? Where did the gigapan author get his pics? No matter how you look at it, something is just wrong.