Taking their photos in this state helped her feel close to them, she said.
The book also includes a number of global landscapes. Her love of this kind of photography began as she was scouting for locations for photo shoots. She really enjoyed this because it reminded her of her childhood, moving from place to place as an Air Force brat.
"It's like being in the car with your family," she said.
But she discovered that she preferred taking the photos of the locations "without the subject."
She showed slides of the great portrait photographer Richard Avedon whom she called a "genius and a great communicator."
"As soon as you engage with someone, their faces change and he knew that," she said.
In a photo she took of him for an award, she described the paradox: He was sick and looked frail and was concerned he'd look weak in the photo. Leibovitz wanted to portray his truth but wanted him to be happy. In the end her allegiance was to her friend. He later wrote to her: "Thank you for taking care of me."
Leibovitz said she does not believe she is a good communicator. She prefers looking at someone to speaking with them when photographing. Sontag, she said, was always pushing her to be better, to be more in control, to take more photos.
The controversial shot of Demi Moore for the cover of Vanity Fair wasn't a planned one, she said. Originally, the now-famous nude photo was taken just for Moore and husband Bruce Willis. But as she looked at it, Leibovitz told the Vanity Fair editor, "This could be a great cover." As the editor decided whether or not to use it, Sontag even called in with her vote.
"It was radical," said Leibovitz. "At the time, there hadn't been anything like it. I was quite taken in by it."
As a child, Leibovitz said her parents always wanted her to smile in photos.
"We had to always...look happy. I thought that was fake," she told the crowd with a smile.
Describing herself as a non-journalist, she said her role is "to express a point-of-view."
In a recent radio interview with National Public Radio, the photographer explained that in the early 19th century, it was a tradition to take the photos of loves ones who passed away as a "remembrance."
And although she didn't have a problem taking the pictures of Sontag and her father after they died, she was concerned with how the public may interpret it. Now, she said, the pictures and the book are "a keepsake" for her.
"It's the closest thing to who I am that I've ever done," she said as she concluded her presentation.
An exhibition of Leibovitz's work from the book opens Friday and runs through January 21, 2007 at the Brooklyn Museum in New York City.