Cameras have become ubiquitous in the security-focused, post-9/11 world. If you live in a big city, you're probably being captured by cameras multiple times every day. London has more than 400,000 cameras in place, according to a 2012 estimate. Chicago boasts more than 17,000.

But if you really want to see where this is leading, go to China. The authoritarian state is proudly creating "the world's biggest camera surveillance network," which uses facial-recognition technology to keep track of its citizens.

So far, the Chinese network has 170 million CCTV cameras installed and operational across the country, and that's just the beginning. The government plans to install more than 400 million more cameras in the next three years.

Law-enforcement officials in the Chinese city of Guiyang were happy to demonstrate the network's effectiveness for a recent BBC report. (Watch the report below.)

"Their vast digital catalog contains the image of every Guiyang resident," the British broadcaster points out. The city has more than 4 million residents.

The police in the city say they can match citizens' faces with their cars and track back their movements, day by day, for a week.

For the BBC report about the camera network, police officers added to their database a photo of British reporter John Sudworth and then set him loose in the city. As he moved through the center of Guiyang, a seemingly anonymous figure in a sea of people, officials "flagged [him] as a suspect," and the hunt was on.

It didn't take long -- seven minutes, to be exact. A camera quickly identified Sudworth as he walked along a busy street and relayed that information to nearby police officers, who surrounded the reporter as he walked into a bus station.

Welcome to the future.

-- Douglas Perry