Montreal police have begun warning motorists against the use of traffic-camera-evading spray-on licence plate films, reports CBC News.

Spray-on films such as PhotoBlocker are highly reflective to direct sources of light, thus blinding traffic cameras accompanied by strobe-lights, which most speed trap and red-light cameras are.

In normal ambient light conditions, however, the spray-on film is not visible, and is thus undetectable under most circumstances.

The purchase of highly-reflective sprays is not illegal, as they have some practical, lawful uses, but, much like some similarly semi-transparent licence plate covers designed to block traffic cameras, they are illegal to use on your vehicle.

While the penalties vary from province to province, motorists caught using reflective sprays can be fined up to $500 in some jurisdictions, like Quebec.

Inspecteur André Durocher of the Montreal police traffic safety division said in an interview with CBC Montreal’s Daybreak program that two different articles of Quebec’s Highway Safety Code apply to camera-blocking sprays, including Section 333, which prohibits any interference with the operation of government traffic camera devices; and Section 334.1, which grants the police the authority to remove or order the removal of any object, material, or device that interferes with traffic cameras, at the vehicle owner’s expense.

Durocher confirmed that many traffic camera setups take photos of both the offending vehicle’s licence plate, as well as the driver’s face.

The dual method means police are then able to identify the drivers of vehicles with camera-blocking sprays applied, presumably through the use of facial recognition software, and send them a fine.

(CBC News with photo from Universe Optics)