Facial recognition software, which American military and intelligence agencies used for years in Iraq and Afghanistan to identify potential terrorists, is being eagerly adopted by dozens of police departments around the country. It is being used with few guidelines and with little oversight or public disclosure. Facial recognition ... is among an array of technologies, including StingRay tracking devices and surveillance aircraft with specialized cameras, that were used in overseas wars but have found their way into local law enforcement. The F.B.I. is pushing ahead with its $1 billion Next Generation Identification program, in which the agency will gather data like fingerprints, iris scans and photographs, as well as information collected through facial recognition software. The F.B.I. system will eventually be made accessible to more than 18,000 local, state, federal and international law enforcement agencies. But people who are not criminal suspects are included in the database, and the error rate for the software is as high as 20 percent - meaning the authorities could misidentify millions of people. Among the cities that use facial recognition technology are New York and Chicago, which has linked it to 25,000 surveillance cameras. In many ways, though, San Diego County is at the forefront. Here, beat cops, detectives and even school police officers have been using hand-held devices to create a vast database of tens of thousands of photos of people - usually without the person's consent.