There is a cute optical (more of a brain) illusion that is triggered when the source of light is at an “unusual” angle with respect to the object. Looking at an image taken from a rough surfaces that is illuminated from below usually triggers this. It messes with the brain’s bump and dent recognition probably because our brain is used to light shining from “above” and shadows being cast downward.

For me that is a great challenge! Some pictures of Mars and Moon are out there that I can’t even wilfully see concave craters in them! The only thing I see is a bunch of “topologically wrong” bumps!!! 😀 Bumps that under close observation… do not cast shadows themselves… spoooky!