Whilst working on the visionary all-seeing eye for this post on phallocentric visual regimes at junk for code, I came across this book by Sarah Kofman. The blurb says that this text offers an extended reflection on the metaphor of the camera obscura as a mode of visual representation.
Kofman contrasts the mechanical function of the camera obscura as a kind of copy machine, rendering a mirror-image of the work, with its use in the writings of Marx, Nietzsche and Freud. In the camera obscura the image is always upside-down.
From memory Marx in the German Ideology uses this metaphor to explain the idelogy as inversions of the truth of capitalism established by social science (ie., historical materialism).Ideology represents reality in an inverted form; as a false consciousness that represents things 'upside down.
I presume the camera obscura metaphor in Freud's psychoanalytic, consciousness-centered notion of the 'human' refers to the unconscious as the dark room contrasted with the light of transparent vision of consciousness. Or, more complexly, Freud used the metaphor of developing a positive from a negative image in which the chamber of the becomes a series of chambers with negatives and positives, movements and repressions, screenings for and from the eye of consciousness.
For Nietzsche the camera obscura is a "metaphor for forgetting." Forgetting involves being attentive to the needs of the present and able to distinguish between what in the past is advantageous and what is disadvantageous for life. Thus "active" forgetting is a selective remembering, a recognition that not all past forms of knowledge and not all experiences are beneficial for present and future life.