This series of images was captured back in 2004 by NASA's first Mars rover, Spirit. Links to original NASA photos are here, here and here.
The shooting location is in Gusev Crater, not far from the Adirondack rock, which was the first Martian rock studied by the rover.
In the middle of the sandy field there are two stones, one flat and with an evenly chopped off edge, and the second, too, seems to be chopped off and surprisingly looks like a petrified log.
This similarity is best seen in black and white, where the entire log is visible. It is darker than the first stone and has jagged potholes.
But the most interesting thing about this stone is not even its log-like shape, but a very even rectangular depression. Could such a hole have formed naturally or is it someone else's handiwork?
The hole is about 4 inches by 6 inches (10 by 15 cm) and some of the ufologists even saw not a hole in it, but … a door. And given that earlier in the photographs from the vastness of Mars we saw a couple of times something similar to tiny men, then maybe this "log" is someone's home?
Promotional video:
