Inside a dimly lit supply shed at the rear of the San Dimas sheriff's substation, an artist of talent and perhaps criminal genius is painting the Mona Lisa. Or an impressive copy of it, at least.

The painter is Anthony Gene Tetro, 43, described as the nation's most prolific art forger when he pleaded no contest in February to forging works by the likes of Marc Chagall, Joan Miro, Norman Rockwell and Salvador Dali.

Superior Court Judge Michael Tynan in April ordered Tetro to produce art--original art--for the public. Tetro is in a six-month work-release program at the San Dimas station in which he paints prototypes for traffic safety murals.

But even as he serves a sentence designed to punish a multimillion-dollar forger, Tetro clings to what he calls his true calling:

"I'm a copyist. I always have been and I always will be. I never had a style of my own. I never wanted to be a famous artist. I just like to paint," Tetro said.

Take the Mona Lisa portrait on the easel in his makeshift studio, for example. In his version of the Da Vinci painting, the ubiquitous lady sits behind the wheel of a red Ferrari, with a seat belt strapped across her. In the passenger seat, a smaller Mona Lisa is tucked in a child-safety seat.

It is a whimsical approach to promoting seat belts and safety seats, perhaps, but it was not Tetro's idea. The credit goes to Jan Nichols, the director of the sheriff's traffic safety project who oversees Tetro.

Other murals in the works, including one of a Statue of Liberty holding a "slow" sign, were also conceived by others and then painted by Tetro.

"If you give him ideas and tell him exactly what you want, then he can come up with good stuff," Nichols said.

Tetro, a former furniture salesman and the son of a New York house painter, said he has never painted truly original work, and he doesn't intend to begin now.

"I paint what I'm asked to paint. I don't see why that should change now," he said. "To me it was a job. It's what I do, and I wasn't moved by it."

But as art gained new popularity in the '80s, it was a job that made Tetro an increasingly wealthy man.

He combined his ability to copy anything, including an artist's signature, with his own special printing method for reproducing lithographs, and soon his imitations were in high demand by individual buyers and art dealers alike.