I was just rereading Barthes now classic essay "Rhetoric of the Image"
when I got your message. He outlines a semiotics of images by analyzing
an advertisement and ends up discussing the rhetoric of images. There's
also John Berger's "understanding a photograph" ; it's an easy to read
discussion of photography's problematic relationship to fine arts and
Berger's method of reading meaning from photographs. There's also
"A short History of Photography" by Walter Benjamin. He does a kind of
Marxist social history of the medium and ends with the prescient notion
that those who will be considered illiterate in the future will be those
who are ignorant of photography.... These are older readings but they might
You can find them all in a collection edited by Alan Trachtenberg
entitled classic Essays on Photography.