“It is often said that it was the painters who invented Photography (by bequeathing it their framing, the Albertian perspective, and the optic of the camera obscura). I say: no, it was the chemists. For the noeme “That-has-been” was possible only on the day when a scientific circumstance (the discovery that silver halogens were sensitive to light) made it possible to recover and print directly the luminous rays emitted by a variously lighted object. The photograph is literally an emanation of the referent. From a real body, which was there, proceed radiations which ultimately touch me, who am here; the duration of the transmission is insignificant; the photograph of the missing being, as Sontag says, will touch me like the delayed rays of a star.”

—Roland Barthes, Camera Lucida, p. 80–81

For noeme, see this.

op. cit., p. 5, p. 111