An emerging trend in video surveillance technology could help tip off school leaders to potential acts of theft or violence before they even happen.

Researchers and security companies are developing cameras that not only watch the world but also interpret what they see. Soon, some cameras might be able to find unattended bags at airports, guess your height, or analyze the way you walk to see if you're hiding something.

Most of the cameras widely used today are used as forensic tools to identify perpetrators after the fact. To stop an act of theft or violence before--or while--it occurs, you'd need to be watching the camera at the time. But the latest development in surveillance technology, known as "intelligent video," could transform cameras from passive observers to eyes with brains, able to detect suspicious behavior and potentially prevent crime before it occurs.

Surveillance cameras are common in many cities, monitoring tough street corners to deter crime, watching over parking lots or sensitive government buildings, and even catching speeders. Cameras are on buses and in train stations, schools, and stores. Most feed video to a central control room, where it is monitored by security staff.

The latest innovations could mean fewer people would be needed to watch what these cameras record, making it more feasible to install more cameras throughout a school building or other institution.

"Law enforcement people in this country are realizing they can use video surveillance to be in a lot of places at one time," said Roy Bordes, who runs an Orlando, Fla.-based security consulting company. He also is a council vice president with ASIS International, a Washington, D.C.-based organization for security officials.

The advancements already have been put to work. For example, cameras in Chicago and Washington can detect gunshots and alert police. Baltimore installed cameras that can play a recorded message and snap pictures of graffiti sprayers or illegal dumpers.

In the commercial market, the gaming industry uses intelligent camera systems that can detect facial features, according to Bordes. Casinos use their vast banks of security cameras to hunt cheating gamblers who have been flagged before.

In London, one of the largest users of surveillance, cameras provided key photos of the men who bombed the underground system in July 2005 and four more who failed in a second attempt just days later. But the cameras were only able to help with the investigation, not prevent the attacks.

Companies that make the latest cameras say the systems, if used broadly, could make video surveillance much more powerful. Cameras could monitor airports and ports, help secure schools and homes, and watch over vast borders to catch people crossing illegally.

Intelligent surveillance uses computer algorithms to interpret what a camera records. The system can be programmed to look for particular things, like an unattended bag or people walking somewhere they don't belong.