Thanks Xiriux, I didn't check it in 3D as there isn't right image for this particular left. But there are also 2 pairs available with different time stamps and I should have used them instead to view the anaglyph.
You're right, what I thought was a crevice in the stone, is infact a shadow on the side of it. It can be seen much clearer in 3D.
-- Edited by Humanoid on Friday 9th of October 2009 08:05:10 PM
It is no other than shadow and stone. Check it in 3D! The dark patch with strange form is the projected shadow of the big stone. The Sun is on zenith. In its shadow lies a small stone with lightened end. That is the "face".
This is quite an interesting image from sol 413? As seen below, there is something sticking out of the crevice, with its lenght partially shadowed inside?! Geological feature? Don't think so..