I'd never heard of this photograph until a few days ago. And I have to echo everyone who has said how disturbing it is. It haunted my dreams the first night. I've been trying to figure out why.
First of all, the subject isn't looking at the photographer. Normal subjects are responding to the photographer, looking at them, smiling, posing for them, some acknowledgment of their presence, however subtle. The person in the photograph, if they are alive, are completely focused on their survival, pain, feelings of shame or fear, I'm not sure what, but it's on whatever they're going through in the moment. If they are deceased, then they died in a state of fear, pain, shame, some negative emotion. There is no sense of fun, experimentation, it's as though they've been compelled, through coercion or against their will.
Second, as others have observed, the location is unusual as it appears to be hidden, in the undergrowth, under branches, away from prying eyes. Someone who did a back bend under branches would risk being poked in the eyes, face, in your torso, armpits. It doesn't make sense unless you or the photographer is trying to conceal what you're doing or your presence there. If they're in a location they aren't supposed to be, you wouldn't do a backbend, unless you were adding an element of risk of being caught. You would take a photograph and go.
Third, there is nothing animated about that face. I did an experiment by holding up a hand mirror to my face while I was hanging my head upside down. Gravity takes over, the cheeks and the mouth sag down, the eyes and mouth become narrow, thins out the face, but doesn't raise the eyebrows. I'm old, so things sag more. The person in the photograph is obviously young, minimal sagging, but gravity will probably change how wide the eyes and mouth are. Especially since the person is not smiling.
There is a dark, well defined and straight shadow across the person's face. It could be a utility pole, a fence pole, a camera stand, someone standing between the person and the sun. It is so straight that I think it's an inanimate object, as opposed to a person.
There is color/stain an inch or more beyond the hairline. It reminds me of coloring my hair. My stylist makes sure she gets the hairs on my hairline by extending the color beyond it by an inch or more. I also notice a typical men's receding hairline pattern around the temples. Not to say that is what it is, but the pattern of the hairline coming to a point at the temple area looks masculine to me. As bizarre as it sounds, it looks like a color job. Plus, the hair that falls from the head doesn't fall straight down, it falls as though there is product on the hair; color, gel, mousse, hair oil, something that flattens the crown hair against the top of the head. There is a second line of color, whether it's dried blood, color, blood pooling in the head, it looks like a stain regardless. It roughly follows the first line closer to the hairline.
I can't imagine coloring your hair in the middle of the woods. Perhaps those upthread are correct. Someone has been hit in the head and stages of bleeding has caused the staining. It's bizarre and disturbing regardless.
All just my opinions. Nothing is stated as fact. I am open to all interpretations. Just here to speculate.