Howard S. Becker quotes:

Laymen learn to read photographs the way they do headlines, skipping over them quickly to get the gist of what is being said. Photographers, on the other hand, study them with the care and attention to detail one might give to a difficult scientific paper or a complicated poem.

Every part of the photographic image carries some information that contributes to its total statement; the viewer's responsibility is to see, in the most literal way, everything that is there and respond to it. To put it another way, the statement the image makes - not just what it show you, but the mood, moral evaluation and casual connections it suggest - is built up from those details. A proper 'reading' of a photograph sees and responds to them consciously.

Photographers learn to interpret photographs in that technical way because they want to understand and use that 'language' themselves just as musicians learn a more technical musical language than the layman needs. Social scientists who want to work with visual materials will have to learn to approach them in this more studious and time-consuming way.