GLADSTONE, Mo. -- The use of red-light cameras is spreading, even as people question the legality of the technology.

Gladstone is the latest metro-area city to approve the cameras, which catch drivers who run red lights.

Recently, the Minnesota State Supreme Court ruled the red-light cameras are unconstitutional. Minnesota justices ruled they are a violation of privacy and the cameras violate the presumption of innocence.

However, the cameras continue to spread in the metro area.

In Sugar Creek, there is a red-light camera on Highway 291. Police Chief Herb Soule said about 150 traffic tickets have been generated each month from the camera.

Before they had the camera, police rarely wrote tickets for red-light runners because they didn't have enough staff, Soule told KMBC's Micheal Mahoney.

Soule said the camera was installed for public safety reasons.

Critics said the red-light camera was installed for monetary reasons. Mahoney reported that in Sugar Creek and in other cities, the manufacturer will install the camera, and take a cut of the ticket.

Gladstone and Kansas City have approved but not installed cameras. Independence and Oak Grove are considering them.

In Kansas, Olathe and Overland Park tried out the cameras, but they don't have them now.

In Minnesota, the cameras were ruled illegal because police issued tickets based on the license plate without proof of who was driving.

"In Missouri, we issue the ticket to the owner of that plate number. If it's not them, then tell who it is and we'll give the ticket to them," Soule said. "It's like a parking ticket. It's your car, so it's your responsibility."

Red-light cameras are already in Springfield, St. Louis and its suburbs.