Enter the nightmare
Entering a painting, or a mirror, or a television set, is practically a sub-genre of fantasy fiction. It's given a pretty horrifying turn in this tale from 1954's Journey Into Fear #19. "Doorway to Death" was done by the Jerry Iger studio for the Canadian publisher, Superior. Most of the stories they turned out are somewhat bent, but in interesting directions. Sier DeFerrac, the artist in the story, has skeletons in his closet. Literally.