Hallucination Imagery
As most of the characters in A Scanner Darkly are users of Substance D, they experience highs and hallucinations that are in keeping with the nature of the drug. For example, the book opens with a scene of Jerry Fabin freaking out about all the tiny bugs ("aphids") crawling in his hair and all over his body, all of which are clearly hallucinations. This particular hallucination even extends to Charles Freck, a fellow user. Such visions are common in the book; another particularly striking example is when Freck takes a massive dose of hallucinogens and watches an angel descend from heaven to read him all of his sins from a massive scroll.
Dilapidation Imagery
Substance D is a big problem in this fictional society, and it's taken its toll on the environment and populace: most of the addicts are described as such, with torn, dirty clothing, disheveled looks, and neglected physical states. Their living environments, as well as the general city streets and non-segregated public places, are grungy and unpleasant; clearly the dilapidation caused by Substance D is psychological as well as physical.
Surveillance Imagery
As a narcotics operative, Arctor plants surveillance devices and spends a considerable amount of time watching the footage from these hidden cameras. The sense of surveillance pervades the entire book, making everything seem suspicious and vulnerable to the leak of information. The imagery of spying is particularly noticeable and unnerving, especially when Arctor watches the footage of his sexual encounter with Connie.
Blurriness Imagery
As Arctor consumes more and more of Substance D, it becomes clear that his addiction is altering his mind in a detrimental way. His mental acuity fades into fuzziness, and the lines of his belief and reasoning skills become seriously blurred. This confused blurriness is especially evident in the imagery of Arctor's scramble suit, which disguises his identity by flashing a different avatar image every nanosecond, making him everyone and no one at the same time. The sense of confusion and uncertainty that Arctor's appearance gives off reflects his internal blurriness, a condition that only worsens as the novel progresses.
