Cindy Crawford says wrote book to mark 50th birthday

American model Cindy Crawford says she decided to write a book to help mark her upcoming 50th birthday.

Crawford celebrated the release of "Becoming" with a book signing in New York on Tuesday.

The 200-plus-page book features more than 100 photos of Crawford, who turns 50 in February, including some from her personal archives and professional shots.

"A couple of years ago we were talking about my 50th birthday coming up ... and we just hit upon this idea," she said.

"Photographically I wanted to celebrate where I've been. But also I wanted to celebrate the lessons I learned along the way."