Every picture tells a story. But what story does it tell? Often, Errol Morris reveals, it's not the one we think; at the very least, the story is more complicated and nuanced. In "Believing Is Seeing: Observations on the Mysteries of Photography," six essays that originally appeared in the New York Times' Opinionator blog are collected into a deeply interesting and coherent whole. The work's title succinctly summarizes the central premise that links all six: "Our beliefs do not determine what is true or false. They do not determine objective reality. But they can determine what we 'see.'"

Morris' observations on the mysteries of photography are equally observations on the mysteries of representing, interpreting, seeing and knowing.

This will come as no surprise to those who have followed Morris' career as a documentary filmmaker. He called his most celebrated film, "The Thin Blue Line," "an essay on false history" in which "a whole group of people, literally everyone, believed a version of the world that was entirely wrong."

Note that word, "wrong." Unlike a number of writers (and filmmakers), Morris does not shy away from such judgments. We can't interpret history any way we feel like it, he says, because "there is a world out there where things happen. And a world that we can actually know in some way." Like his films, "Believing Is Seeing" is a means of working through this conviction, with the photos providing an occasion to think about "some of the most vexing issues in photography -- about posing, about the intentions of the photographer, about the nature of photographic evidence -- about the relationship between photographs and reality."

In each chapter, Morris looks at documentary photographs -- really looks at them, both literally and figuratively -- to determine the truest story each can yield. Some images, like the paired pictures from Abu Ghraib and an iconic photo of a Mickey Mouse toy in the rubble of a bomb site (Lebanon 2006), are likely to be familiar to readers; others, like an American Civil War era ambrotype of three small children, will be new to all but a few specialists. Morris interrogates these images the way a detective grills a suspect (and, in fact, Morris did once work for a private detective agency): Who took the picture? When? Why? Under what conditions? For what purpose?

In the book's preface, he encourages us to read the essays as "a collection of mystery stories," and Morris himself makes a quirky, intelligent, obsessive Hercule Poirot (without the smugness).

And what a range of evidence this fanatical Detective Morris presents: a sun map of Sebastopol, an illustrated discussion of the difference between a genuine (Duchenne) smile and a social smile, a brief gloss on archaeoastronomy, the true story of an orphanage director breaking bad. Once you start really looking at things, there's no telling where you'll end up, but the journey itself is so pleasurable, so fascinating, that the end point really doesn't matter.

Patricia Hagen teaches English at the College of St. Scholastica in Duluth.