Police in London will deploy facial recognition technology in a two-day trial starting on Monday.
Covering London's Soho, Piccadilly Circus and Leicester Square, the tech will scan faces in crowds and run them against a database of people wanted by London's Metropolitan Police and the courts.
If the technology alerts officers to a match, police on the ground will review it and carry out further checks to confirm the individual's identity.
The scanners will be deployed for around eight hours per day and positioned visibly alongside a uniformed police presence. The rollout is part of a wider policing strategy to reduce crime and violence in Westminster.
Passers-by are entitled to avoid being scanned, and all footage will be deleted immediately after the trial. Faces matching the watchlist will be kept for 30 days.
The Met has made efforts to inform the public about its use of the technology by handing out leaflets and placing posters in the areas where it will be deployed. Officers will also engage with members of the public to explain the process.
However, the use of the technology has faced criticism, with campaign group Big Brother Watch (BBW) raising £6,685 ($8,440) in a crowdfunder to launch a legal challenge against its deployment.
BBW says it used the U.K.'s Freedom of Information laws to obtain police figures which showed 100 percent of matches made by the scanners since May have been inaccurate.
"The police's use of this authoritarian surveillance tool in total absence of a legal or democratic basis is alarming," Silkie Carlo, director of BBW, said in a statement. "The fact that it has been utterly useless so far shows what a terrible waste of police time and public money it is. It is well overdue that police drop this dangerous and lawless technology."
Ivan Balhatchet, strategic lead for the project, said the Met Police had committed to four more trials of facial recognition technology by the end of the year.
"We continue to engage with many different stakeholders, some who actively challenge our use of this technology," he said in a press release. "In order to show transparency and continue constructive debate, we have invited individuals and groups with varying views on our use of facial recognition technology to this deployment."
The police force will analyze data collected in the trial to assess whether the technology is a useful tool for deterring and tracing criminals. Public consultations are also due to be held so police can canvass the public over concerns about its use. Future deployments being considered include sporting events, music festivals and transport hubs.
In May, U.K. Information Commissioner Elizabeth Denham said the use of the technology would only be legal if police forces could prove using it in public spaces was resolving the issues it aimed to address.
Facial recognition technology isn't only being applied to policing, with biometrics increasingly being used by private firms.
Australian airline Qantas announced in July that it would use the technology for passenger identification. Sydney Airport's CEO said at the time that in the future "your face will be your passport."
Last week, car rental company Hertz unveiled its first biometric lane at Atlanta International Airport. The lanes allow customers to use facial scanners instead of showing a physical form of identification, which Hertz said makes renting a car up to 75 percent faster.