As digital cameras and projectors revolutionize the movie business, governments around the world must band together to crack down on a growing side-effect of the digital wave — DVD and Internet movie piracy, the head of the U.S. film industry said Wednesday.

At the Cannes Film Festival (news - web sites), Jack Valenti and French industry leaders agreed on the need for a global alliance against piracy. Copied video cassettes have already harmed the industry, and Internet and DVD piracy are far more dangerous, he said.

"The difference between digital piracy and analog piracy is like the difference between lightning and lightning bugs," the president of the Motion Picture Association of America said in a telephone interview.

When pirates make video cassettes, the quality fades with every copy. The U.S. film industry loses dlrs 3.5 billion a year in revenues from analog piracy alone, Valenti said.

But with digital, "you can make a thousand copies and the image is just as pure," Valenti said. "Anything digital never wears out."

This year, the Cannes festival has been showcasing directors who found innovative uses for digital filmmaking. For example, one film in competition, "Russian Ark," used a single Steadycam shot to film the entire 90-minute movie.

The festival also equipped two of its theaters with digital projectors, which use tiny mirrors and prisms instead of the traditional film reels.

But Valenti's focus was on digital's disadvantages. He met with the director of France's National Cinematography Center and the head of Gaumont, a French production company and cinema chain, to talk about solutions.

Worldwide, "copyright laws must be stern and clear" and allow for severe punishments for pirates, namely prison sentences, Valenti said. Too many governments that already have strict copyright laws are too lax in enforcing them, he said.

If pirates are merely fined, "the fine just becomes a regular part of doing business," Valenti said.

David Kessler, director of France's National Cinematography Center, says Internet piracy will harm the movie business in the same way it has already harmed the music business unless countries worldwide agree on measures to tackle it.

"Right now it's more difficult to download movies than music," Kessler said in an interview. "In the future it will be just as easy."