And beginning this summer, the cameras watching us are going to be made "smarter." You can have a camera on every corner, but who's watching what the camera sees? The technology now exists to tell the camera what to look for. It's called "video analytics" and it's about to be married to Operation Virtual Shield - Chicago's ever-growing network of public surveillance cameras. If you walk down LaSalle Street, several cameras could be watching you. They're everywhere. They're multiplying. Several thousand cameras are now capable of sending live pictures into a room - the operations center at the city's Office of Emergency Management and Communication. There's no way that human beings can effectively watch all those feeds, so enter video analytics. By programming algorithms, you give the camera intelligence. "We actually can tell the camera, 'This is precisely what we're looking for.' The camera will watch for that circumstance, and when that circumstance occurs, comes back to the human being whether they're watching that camera or not - with an alert," said OEMC director Jim Argiropolous. Say you want to monitor activity at the base of the Sears Tower. An operator can use his mouse to create a trip wire, or in this case, a rectangle that the camera will see. The cameras can be programmed to watch for things like unattended backpacks or parked cars. Of course, it may be just a cabbie dropping a fare, but the camera will see, and the operator is watching. All the camera feeds go into a 60-terrabyte storage bin, where the video is routinely held for 30 days. "You can retroactively go back and do searches on that video for an event that occurred historically," said Roger Rehayem, IBM. Say there's a witness description of a blue car involved in a robbery, and that it may have passed over the LaSalle Street bridge where a camera is posted. Analytics can be used to search all the video from that camera for a car matching the description. Up come thumbnails, each with video of a potential match. You can freeze it, enlarge it, maybe get a license or another marker and maybe catch a bad guy. The technology will grow and so too will the number of cameras. But ultimately, how many cameras do we need, at what cost and how effective are they in fighting crime? Great Britain has more cameras than anywhere else. They've helped solve some major crimes, but studies there are mixed on whether they actually prevent crime. In the U.S., there've been few, if any, detailed studies of public surveillance cameras. "People get so enamored with this technology that has such promise that they quickly adopt it without thinking about whether it has an impact," said Dr. Nancy LaVigne, Urban Institute. LaVigne is launching a study of public surveillance cameras in four cities. Chicago is one of them. She'll be focusing on police department cameras here - nearly 700 of them - that now watch Chicago neighborhoods. Do they prevent crime? Do they displace it - in other words just move it somewhere else? Does camera footage hold up in prosecutions? Is there a cost-benefit ratio? "I have reason to believe they're effective in certain contexts, and so our goal would be, 'here's how you can make them more effective,'" said LaVigne. Chicago police say their street corner cameras have not only discouraged crime but have directly led to arrests in some violent crimes, including the murder of a teenager last summer. But research on the effectiveness of public surveillance cameras nationwide has not yet taken shape. Some smaller cities have found it to be cost prohibitive.