Cameron Diaz denied it was her signature on the release form

John Rutter told Los Angeles Superior Court he had an assistant deal with release forms, but he assumed Ms Diaz's signature was authentic.

By offering to sell the pictures back to the actress in 2003, he was merely giving her "right of first refusal".

Mr Rutter, 42, denies forging Ms Diaz's signature and attempted grand theft.

Prosecutors allege that Mr Rutter forged Ms Diaz's signature on the photo release form and tried to sell the photos back to her for $3.3m (�1.9m).

Deputy District Attorney David Walgren asked Mr Rutter whether he now believes the signature is fake.

"It looks like that," the photographer replied.

Not responsible

Mark Werkesman, Mr Rutter's defence lawyer, suggested others may have been responsible for the forgery.

Under cross-examination on Tuesday, Frank Moore - Mr Rutter's former agent - said he was unsure if he had obtained a signature from the actress.

Rutter contacted Diaz ahead of the Charlie's Angel sequel

The photographs were taken in 1992, before Ms Diaz's rise to fame in 1994 comedy The Mask.

Mr Rutter is accused of threatening to sell them to the highest bidder unless she agreed to pay him.

The 32-year-old actress told the court she had not signed a release form for the pictures, while expert witnesses presented evidence suggesting her signature had been forged on the document.

The judge has issued a permanent injunction forbidding him from distributing the photographs.

Mr Rutter is expected to testify again on Thursday. If convicted of the charges, he could face a jail sentence of up to six years.

Closing arguments are expected on Friday.