In Camera Lucida, Barthes' quasi-scientific explication of the photographic process introduces the idea of the referent as revenant.

"What does my body know of Photography? I observed that a photograph can be the object of three practices (or of three emotions, or of three intentions) : to do, to undergo, to look. The Operator is the Photographer. The Spectator is ourselves, all of us who glance through collections of photographs - in magazines and newspapers, in books, albums, archives... And the person or thing photographed is the target, the referent, a kind of little simulacrum, any eidolon emitted by the object, which I should like to call the Spectrum of the Photograph, because this word retains, through its root, a relation to "spectacle" and adds to it that rather terrible thing which is there in every photograph: the return of the dead." (Barthes, p.9, 1980)

The referent is a revenant - like the ghost of Hamlet's father - who always begins by coming back. That, as Derrida reminds us, is the nature of ghosts and of language. They can only exist as by virtue of their return. The apparition is the mark of an absent present.