What do you see when you look at a photograph? In his fascinating study of the act of looking, the filmmaker and writer Errol Morris considers a half-dozen images and questions the prevailing view “that photographs provide a magic path to the truth.” Rather, Morris treats each picture as a “mystery,” and shows that a large part of what we get out of one depends on the assumptions—about subject, context, photographer’s intention—we bring to it, that in fact Believing is Seeing (Penguin Press, $40). Morris is an intrepid detective, even traveling to the Crimea to see the site of an 1855 war photo by James Fenton. He similarly investigates the identity of the hooded man in an Abu Ghraib image, talks to a photographer who covered the 2006 Israeli attacks on Lebanon, tracks down the descendents of a dead Civil War soldier identified only by the ambertype of three children he had in his pocket. The book becomes a collection of evidence, including maps, diagrams, doctored images, along with letters and interviews. Ultimately, Morris’s questions overshadow any answers. Oh, and the truth? In photos that’s “an elusive notion. There may not be any such thing.”