The FBI is spending $1 billion to put together a facial recognition database that will let it spot suspects using footage from public security cameras. The new system would mark a giant leap forward for the bureau, which for decades has been using fingerprints and mug shots to ID suspects. How will it work, and should ordinary citizens be worried about privacy invasions? Here, a brief guide:

How would the system work?

The program, called Next Generation Identification, is basically a more comprehensive version of the FBI's fingerprinting database, which worked about the same way in 1999 as it did when the FBI began collecting prints, in 1924. To build the new database, police will start collecting more identifying information, from iris scans to DNA analysis to voice identification, so that in the future, federal agents will be able to use public cameras to pick out suspects and persons of interest from a crowd.

Can it really spot bad guys in a crowd?

Yes. In 2010, tests found that some computer algorithms were able to match a person on camera to the right mug shot on file 92 percent of the time. The system is also able to use profile shots to spot people even if they don't look straight into the camera.

When will it be ready to use?

There's already a pilot program underway in select areas, but the full rollout isn't expected until 2014. Right now, the system is only hooked up to law enforcement databases, so agents can only sift through the details of people with a criminal record. At some point, however, the database could be linked to other government photo databases, so that anyone with a driver's license or other government-issued ID could be caught in the web.

Are privacy activists angry?

Yes. We ought to be very wary of "Big Brother" rolling out a nationwide system to "spy on the entire population," says Sara Reardon at New Scientist. Even if the government doesn't abuse this power, "unauthorized users might be able to hack the system and gain access to sensitive data." It's easy to understand the "hysterics," says Rick Moran at The American Thinker. "You don't have to be a paranoid to ask legitimate questions about where all this is leading." Still, you have to admit that as long as there's oversight to make sure this facial recognition technology isn't abused, it could yield important benefits to us all.

Sources: American Thinker, CNET, Mashable, New Scientist