Diaz is one of Hollywood's highest paid actresses

The Charlie's Angels star told a jury in Los Angeles Superior Court that Mr Rutter's alleged demand for $3.3m (�1.9m) made her "sick to my stomach".

John Rutter, 42, is charged with forging Diaz's signature on a model release form and attempted grand theft.

He denies the charges. If convicted, he could face up to six years in prison.

The photographs were taken in 1992, before Diaz shot to fame in the 1994 hit comedy The Mask.

I wasn't ashamed to be out there like that. It was a professional shoot. Cameron Diaz

Diaz said Mr Rutter approached her about the sale of the photos in 2003 during a promotional tour for Charlie's Angels sequel Full Throttle, claiming he had been offered $5m (�2.8m) by magazines in Europe.

The 32-year-old actress said she was "not ashamed" of the photographs, which showed her posing in leather boots and fishnet stockings in an abandoned warehouse.

"I wasn't ashamed to be out there like that," Ms Diaz told the jury. "It was a professional shoot. It wasn't like in a back alley."

She added that she believed she looked good topless: "At least I have that going for me," she recalled thinking.

However, she maintained that she did not sign any release form giving ownership of the photos to Mr Rutter.

"I have never signed my name like that," said Diaz.

Diaz lent her voice to the box office hits Shrek and Shrek 2

Mr Rutter's lawyer, Mr Werksman, has suggested Diaz wanted to suppress photos that could damage her career.

He told jurors on Wednesday that the case was about "a rich and powerful movie star ... seeking to crush and destroy John Rutter" and "forever bury" embarrassing photographs.

Mr Rutter was "guilty of being a nice guy" for giving Diaz the first opportunity to buy the photos, he added.

The photographs at the heart of the case are being kept under lock and key by the authorities. The judge ordered them to be sealed two years ago - until the dispute is settled.

The trial is expected to last two weeks.