This is pretty amazing -- an online course by The Museum of Modern Art on learning to really understand photographs. The course is free, but for @28 US dollars you can get a certificate of completion, for whatever that might be worth.
“While taking, viewing, and sharing photographs is second nature to many, it is not synonymous with visual literacy. It is our hope that Seeing Through Photographs encourages learners to explore the gap between seeing photographs and truly understanding them.” -- Sarah Meister, Curator, Department of Photography, MoMA
I have only watched the introduction and an interview with Marvin Heiferman so far, both of which were completely absorbing.