I have started to look into other forms of religious imagery and also the concept of hell which seems to be a predominant theme in metal bands art work. Often with demons being a focus.
demonology

diːməˈnɒlədʒi/

noun

the study of demons or demonic belief.

a set of beliefs about people or things regarded as harmful or unwelcome.

The Biblical Doctrine of Hell

http://www.auburn.edu/~allenkc/tbhell.html

http://www.churchofsatan.com/history-sigil-of-baphomet.php
History surrounding the symbols that are used to illustrate and depict satan.

9 Circles of Hell (Dante's Inferno)

http://historylists.org/art/9-circles-of-hell-dantes-inferno.html

http://www.worldofdante.org/gallery_dore.html

http://designyoutrust.com/2016/10/the-devil-and-his-servants-demonic-nsfw-illustrations-from-18th-century-occult-book/

15 Different Interpretations of Hell in Art

http://mentalfloss.com/article/31477/13-disturbing-pieces-art-history

13 Disturbing Pieces of Art from History

"The media is often criticized for showing violent and disturbing imagery. Movies, TV, video games, tabletop RPGs, comic books, and various other things have all gone through periods where they're blamed for exposing children to dark and unsettling things. But as these fine art examples prove, violent and disturbing imagery is nothing new."