Old Magic: The Gathering cards do this all the time, alot of the card art would fit perfectly on some 80s metal album with LOTR-lyrics. There are too many to show but this is a classic:
Also Mignola sometimes has this doomdeath feel in his Hellboy art, like this for example:
More things, alot of those are already rightfully recognized as metal by alot of bands (alot of pictures).
Some art:
Midvinterblot by Carl Larsson:
Asgårdsreien by Peter Nicolai Arbo:
Tors strid med jättarna by Mårten Eskil Winge:
Sorgen by Theodor Kittelsen:
Seventh Seal by Ingmar Bergman has to be one of the most sampled movies in (extreme) metal, the Flagellants are probably one of the most doom metal things outside of doom metal:
Games Workshop is just like Magic the Gathering an endless source of badass metal artwork, for example: