This is a picture of a real human skull I photographed some years ago for a project I never completed.
I borrowed it off a guy for a day and it was slightly odd cycling round town with this thing in my backpack. I was thinking that if I got stopped and searched by the police it was gonna look pretty damn weird. Don't know much about the skull except that it was pretty old - ie. some hundreds of years as I remember.
I'm not really into rules. Use as you want on or off DA. Posting a link here to artwork will give me an idea how useful this is. I have a load more pics of it I'll upload some time, especially if popular.