The woman who is perhaps the most well-known photographer in America — Annie Leibovitz — says it’s impossible to expose the “soul” of a person in a photograph.

“I love to say something new about someone or something that tells a story but I’m not so worried about doing that,” Leibovitz said on MSNBC Monday morning as she promoted her book: Annie Leibovitz at Work.

“You can’t really capture the soul — it’s more about what the subject wants to give you that day.”

Leibovitz has shot celebrities such as Demi Moore, Tina Fey, Madonna and a slew of others during the more than 20 years she’s worked at Vanity Fair, and, later, for Vogue. It’s Leibovitz whom Tom Cruise and Katie Holmes called to take the first public shots of their daughter, Suri.

During Leibovitz’s recent photo shoot with Fey – the “30 Rock” and “Saturday Night Live” star who graces the cover of the January issue of the magazine, complete with a huge American flag behind her — the photographer said she was enthralled by the comedienne.

“I’m so enamored by her … it’s so amazing, the power of comedy,” and how Fey impersonated Alaska Gov. Sarah Palin, John McCain’s vice-presidential running mate this year, Leibovitz said. “I’m just so impressed with the power of comedy.”

She also said “that Hollywood cliché is true” – that some celebrities are just made for the camera.

“You can’t take a bad picture of Johnny Depp, you can’t take a bad picture of Nicole Kidman,” she said.

Included in Leibovitz’s new book are infamous photos such as naked John Lennon curled up next to fully clothed Yoko Ono, taken in 1980 when Leibovitz was working for Rolling Stone. Lennon was shot and killed five hours after the shoot.

In the book, Leibovitz describes how her pictures were made, starting with Richard Nixon’s resignation, ending with Barack Obama’s campaign – and the Rolling Stones tour, The Blues Brothers, Arnold Schwarzenegger, Patti Smith, George W. Bush, Kate Moss and Queen Elizabeth, and everyone in between.

As for the inevitable question of who the most difficult subject was to photograph? Leibovitz on Monday was mum on that, but said the answer to that is in her book.

We’ll be sure to run out and get a copy. Meanwhile, check out wOw’s photo essay and an excerpt from Annie Leibovitz at Work.