Hackers use surveillance images for mischief.

Britain has been crowned the most-watched society in the world. The country boasts 4.2 million security cameras (one for every 14 people). A typical Londoner makes an estimated 300 closed-circuit television (CCTV) appearances a day, an average easily met in the short walk between Trafalgar Square and the Houses of Parliament. Polls seem to reflect the public's fine with it. But how useful is CCTV in stop-ping crime? Not very, says Scotland Yard.

At the same time, a new class of guerrilla artists and hackers are commandeering the boring, grainy images of parking lots and corridors for their own purposes. For about $80 at any electronics store and some technical know-how, it's possible to tap into London's CCTV hotspots with a simple wireless receiver. Dubbed "video sniffing," the pastime evolved out of the days before widely available broadband, when "war-chalkers" scouted the city for unsecured Wi-Fi networks and marked them with chalk. Sniffing is catching on in other parts of Europe, as well as in New York and Brazil, spread by a small but connected community of practitioners. "It's actually a really relaxing thing to do on a Sunday," says Joao Wilbert, a master's student in interactive media, who slowly paces the streets in London like a treasure hunter, watching a tiny handheld monitor for something to flicker onto the screen. These excursions pick up obscure, random shots from restaurants and hotel lobbies, or of a young couple shopping in a housewares department. Eerily, baby cribs are the most common images. Wireless child monitors work on the same frequency as other surveillance systems.

Given that sniffing is illegal, some artists have found another way to obtain footage: they ask for it. In making her film "Faceless," Manu Luksch made use of a little-known British law that requires CCTV operators to release a copy of their footage upon the request of anyone captured on their cameras. She decided to make a feature-length love story. After four years of performing, staging large dance ensembles in public atriums and submitting the proper paperwork, Luksch produced a haunting film and social commentary.

In some cases, video sniffing has morphed into a form of hacking, in which the sniffer does more than just watch. Using a strong transmitter, sniffers can hijack wireless networks and broadcast different images back to a security desk. One organization used the device to broadcast a videogame animation of a spaceship flying over the town with security cameras. A German group of sniffers are using the cameras mounted behind counters at fast-food joints to watch employees. They've broadcast McDonald's to Burger King, Burger King to KFC, and so on.

Most sniffers, hijackers and artists using CCTV are critical of the present level of surveillance and want public discussion of what's appropriate. They say the ability to tap into wireless surveillance systems and take them over points out a flaw in the elaborate security apparatus that has evolved around us.

Anthropologists tell us the act of observation changes what's being observed. Cameras "reorder the environment," says Graham Harwood, artistic director of the group Mongrel, which specializes in digital media. Sniffing and hijacking could become the next high-tech social phenomenon. Or it could disappear quickly once the surveillance industry catches on and beefs up security. But even then, the cameras will remain.