Richard Prince's most famous photograph was made by me.

There are grander and more sublime landscapes - to me. There are more compelling cultures. But what appeals to me about central Montana is that the combination of landscape and lifestyle is the most compelling I've seen on this earth. Small mountain ranges and open prairie, and different weather, different light, all within a 360-degree view.

We know that photographs inform people. We also know that photographs move people. The photograph that does both is the one we want to see and make.

It's a little bit like talking about the life of writing. The life of writing may be about many things, but it always begins with the writer. With the kernel of an idea, or a character, or an idea or a theme, or even an outcome. But for documentary photographers, photographs begin at that intersection of the real world and the imaginative inner world.

I was giving a lecture and I said, that's enough about The Photographic Life, meaning my biography, now let's talk about the life of a photograph. And in that one instant I got the title for a potential next book.

I did a story for the Geographic on Meriwether Lewis and William Clark, and Stephen Ambrose was the writer. He said, "I've got the easiest job in the world. I just have to re-tell the story of the greatest fishing, camping, hunting, canoeing trip of all time. You, Sam, have the hardest job, which is, pretend like nothing has happened in the last 200 years.

Life rarely presents fully finished photographs. An image evolves, often from a single strand of visual interest - a distant horizon, a moment of light, a held expression.