Two forensic experts have testified that a signature on a model release form involving topless photos of Cameron Diaz (search) appeared to be forged, using an autographed publicity photo of the actress.

Photographer John Rutter (search) is accused of trying to blackmail Diaz over the pictures he took in 1992, before she was famous, and attempted to sell back to her in 2003 for $3.5 million, before her film "Charlie's Angels: Full Throttle (search)" was released.

Forensic document examiner Bruce Greenwood, who has analyzed copies of Diaz's writings, testified Monday that the signature on the release form appeared to be forged.

He also testified that the signature on the publicity photo of Diaz and "Feeling Minnesota" co-star Keanu Reeves (search) was a fake.

Greenwood said he noted certain letters in Diaz's name were "slanted completely different" from the handwriting samples that he had received from her.

Diaz testified last week that Rutter told her if she didn't buy the photos, he could sell them for $5 million to buyers he said would use them to portray her as a "bad angel."

Prosecutors said Rutter allegedly showed Diaz the release form when he tried to blackmail her and the actress said it wasn't her signature.

Forensic expert George Reis, who worked for the Newport Beach Police Department for 15 years, also said Diaz's signature was forged and that it appeared the publicity photo was used to make the forgery.

Rutter, 42, is charged with attempted grand theft for the alleged blackmail scheme, forgery for the signature on the form and perjury for declaring in a separate civil case that the signature was authentic. If convicted, he could face up to six years in prison. An extortion charge has been dropped.

His defense lawyer has suggested Diaz wanted to suppress photos that could damage her career.

Diaz, 32, is suing Rutter in civil court. A judge has issued a permanent injunction prohibiting Rutter from distributing the photos.