The celebrated director of such films as The Thin Blue Line and the Oscar-winning The Fog of War investigates some of photography's most iconic, enduring, and mysterious images in Believing Is Seeing from Penguin Press.

Is it true you were once a private eye? Has it influenced how you look at the truth?

It's true I worked as a detective, but I think the desire to investigate things... either you have it or you don't. It's the Dupin or the Sherlock Holmes in me. Almost all of my work has been about this underlying belief that we can figure things out. And every photograph is a mystery. Photographs rip a swatch from the fabric of reality. They decontextualize. But they're still connected to the world, and they tell two stories: one about our belief about images, but also about one moment in history, of something happening at one moment in front of one particular lens. At its heart, this is a romantic book. To try to figure out—what was that world recorded by James Fenton? Or the world of Amos Humiston and the photograph found in his hands on the battlefield at Gettysburg?

Many of these stories first appeared on your blog at the New York Times. When did you realize you had a book on your hands?

When I realized I could actually write. The first big piece I did was on the James Fenton photographs of the Crimean War. You wouldn't imagine that it would be the kind of subject matter that would attract a lot of attention, but it did. The piece—and the book—is about photographs as a way of entering history through something very specific. If you pick up any one of the hundreds of histories of the Crimean War, invariably it will start off with a description of the historical antecedents and gradually and chronologically you will enter in the story. Same with biography; you open one and you're reading about someone's maternal grandparents. What a photograph allows you to do is to enter history in the middle of everything. As I imagine it, you walk into the photographs and start looking around. That's the beginning of a mystery.

It was your investigation into Fenton's photographs—and your team's attempt to establish what time they were taken by analyzing every stone and shadow—that first made the Crimean War real to me, that persuaded me that it actually happened. So as you say, photographs seem to make history not only specific but material.

We're connected through particulars—that's really our experience of being alive. When I ended up in Crimea, I had a map from 1855 with me. I was standing on a hill that the map called Snail Hill. I looked down, and there were little snails all over the place. Later I read a soldier's account of being in one of the trenches on Snail Hill, and he was surrounded by all of the little snails. I felt suddenly connected to history, and connected through particulars, through the odd details.

You're rare in that unlike most people who have written a great deal about photography, you've actually worked extensively with cameras. Photography isn't abstract to you. Has this influenced how you'd read, say, Sontag or Barthes?

I know that Sontag's essay on the Abu Ghraib photos in the New York Times magazine influenced me in so many ways, although I didn't agree with her conclusions. What she didn't do—and what I have tried to do—is accept that photographs are never a given. We may think we know what a photograph means, we may think we know what it's of, but we don't. To me the Abu Ghraib photos are a perfect example of a kind of mystery. What was going on? Were they all taken for the same reasons? Who were the people that took them? Whenever you look at a photograph, you're looking at what is no longer there. The photograph is there, but what was photographed is transient, is gone. Proust had his madeleines. I have my photographs.