Alchemical symbols arranged with alphabetical correspondences. This is available as a free True Font download for your PC at dafont.com. The font is called Agathodaimon - type that in the search box at the site, Another excellent set of characters for secret writing in a Book of Shadows.
The skull is very well proportioned with the woman's head in this picture. The black and white also makes the picture blend better and look more real. The way her hair and makeup has been done compliments the skull.