If you are interested in how to think about photographs when you look at them as well as the history of photography then I suggest checking out the coursera / MoMA online course "Seeing Through Photographs". The current session is already underway but there are several upcoming sessions as well. There are quite a few videos to watch and some serious reading assignments plus quizzes but it's well worth it if you want to become more visually literate. The course is free to take or you can pay if you'd like to get a certificate upon completion. Your choice, which is great.