The image which the narrator returns to again and again in this story is the image of the old man's eye. It is the eye that causes the narrator's blood to boil and that drives him to murder the old man. The eye is described as "the eye of a vulture—a pale blue eye, with a film over it." A vulture is a scavenging bird of prey. It has a rather beady eye, which usually appears rather stern and judgmental. The fact that the narrator imagines the old man's eye in this way suggests that he, the narrator, is perhaps paranoid about being watched and maybe being judged. However, the fact that the narrator says, "I think it was his eye! Yes, it was this!" could suggest that he is simply fumbling for an excuse after the murder, in retrospect, to lend some sort of rationale to the murder beyond his own madness.
Another key image that recurs throughout the story is the image of darkness. The narrator almost seems to luxuriate in the darkness of the old man's room:
I put in a dark lantern, all closed, closed, that no light shone out . . . His room was as black as pitch with the thick darkness.
The narrator likes the darkness because it hides him. If he cannot be seen, then he also cannot be judged. This links back to the idea that the narrator is not comfortable exposing himself to the judgement of others. Darkness is also a common motif, in literature and film, to connote evil. The witch in Disney's Snow White, for example, wears black to indicate her evil character, and the evil characters in Star Wars are collectively known as 'The Dark Side.'
In the fifth paragraph of the story, the narrator describes himself as death:
Death, in approaching him had stalked with his black shadow before him, and enveloped the victim.
The narrator perhaps likes to imagine himself as the personification of death here because it allows him to feel powerful. Death is inevitable and ultimately has power over everyone. The narrator likes to feel as if he has a similar power.
The most enduring image from the story, and the image which, of course, reveals the most about the narrator's character, appears during the story's climax. This is the image of "the hideous heart" beating relentlessly, and louder and louder, beneath the floorboards. This is predominantly an example of aural imagery, or, in other words, an image which engages our sense of hearing as much as or more than our sense of sight. The relentless, agonizing beating of the heart represents the narrator's conscience, or guilt. He seems to be, throughout the story, completely mad, but the fact that his conscience, in the form of this heart, overwhelms him and forces him to admit to the murder suggests that there is just a small part of him which remains sane and perhaps moral.