I'm not seeing a lot of what other people are describing, like I don't see a dog or a bearded guy or a ski-mask guy. I want to see it, but I don't. At least not yet. ;-)
Warning: Graphic sexual language:
To be honest, I think I am seeing a couple things in the picture. Y'all are likely going to think me a pervert, but the 2 things I'm seeing are sexual in nature. It appears to me that the artist was working from photographs. I hypothesize that he had pictures on his computer or cell phone of the woman, because the anatomical & muscular detail, and the play of light and shadow is so precise. The nude photographs themselves may have even been cropped & inserted into the skull pic and then painted over.
What I'm seeing is the picture of a woman's torso & bare breasts which I already posted about earlier. The aereola & nipple facing the viewer is perfectly round and in fact the whole torso & smallish breasts are perfectly rendered in every way. This is painted in orange & yellow.
Also painted in orange & yellow is the other image of the woman's body, below the breast pic, and of about the same overall dimensions. It looks to me like a cell phone pic that a guy took while "being intimate" with a woman from behind. I can see perfectly her back, the shape of her hips, and her hair cascading down past her shoulder blades. Earlier I said I thought this hidden image of a woman's back was probably nothing, but now I do think it's probably an intentional image, like a "sister image" to the woman's bare breast image above it.
I have circled both of the 'nude female" images that I see:
Thanks, HeartGoesOut, for bringing these hidden things to our attention in a big way.