Drivers Try an Anti-Photo Finish

But, he adds, those adjustments aren't usually necessary. "In the case of sprays, we know they don't work . . . and we've tested every spray that's there," he says.

Says Ray Reyer: "That's his perspective. There have been cities and towns that have banned the spray. Illinois just did. The reason they're doing this is because they're losing revenue. Why else would they?"

For some law-abiding consumers, effectiveness may be a moot point. Many jurisdictions insist that such products are prohibited by laws that ban obstructing license plates. Ads for such products typically include a disclaimer about their legality.

Anne Witt, director of the D.C. Department of Motor Vehicles, thinks the products are "not legal in the District." D.C. laws require that license plates be "maintained free from foreign materials and in a clearly legible condition" and ban the attachment of anything that obstructs any part of the tag. The "illegible tag" fine is $50.

The District's automated red-light and speed-enforcement programs are in full gear. Red-light cameras, now at 39 locations, have ticketed more than 450,000 drivers and collected $27 million in fines since the program's inception in 1999, according to the D.C. police Web site. The department's photo-radar speeding program, using mostly mobile cameras, has issued 993,000 tickets and collected more than $53.6 million since it began in 2001 -- including more than $10 million in 2004.

Virginia outlaws any cover that obstructs the license plate, but the law doesn't specify clear spray coatings. However, Tim Murtaugh, spokesman for Attorney General Jerry W. Kilgore, says state law bans "colored glass, colored plastic or any other type of covering" installed over a license plate in a way that alters or obscures. "We believe this would apply" to the sprays, he says.

Scott argues that a loophole makes PhotoBlocker legal. "The law says you cannot obstruct your license plate," he says. "This spray only prevents a flash camera from taking a picture. If you look at it with the naked eye, you can't tell it's on there."

Maryland's law is more specific, prohibiting "use, advertising and sale of license plate covers that distort a recorded image of any of the characters of a vehicle's registration plate recorded by a traffic control signal monitoring system."

Says Kevin Enright, spokesman for Attorney General J. Joseph Curran Jr.: "There is no question that using these products is illegal under Maryland motor vehicle laws."

John Carr, who has maintained a "State Traffic and Speed Law" Web site since 1997, says many states also have "very broad laws" about interfering with police.

But Scott has another point to make: Even if laws target anti-photo sprays, police would be hard-pressed to identify who is using them.

"There is no way to identify which plates are coated and which are not," he says.