The Metropolitan Police is beginning operational use of facial recognition technology across London.
It follows a number of trials of the cameras, which have been criticised by human rights campaigners as a risk to privacy.
Here’s how the technology works, and why it has proved so controversial.
– How does it work?
Live facial recognition (LFR) technology uses special cameras to scan the structure of faces in a crowd.
The system then creates a digital image and compares the result against a ‘watch list’ made up of pictures of people who have been taken into police custody.
Not everybody on police watch lists is wanted for the purposes of arrest – they can include missing people and other persons of interest.
If a match is found, officers in the area of the cameras are alerted.
– How much has it been used?
The Met have used the technology multiple times since 2016, according to the force’s website, including at Notting Hill Carnival in 2016 and 2017, Remembrance Day in 2017, and Port of Hull docks, assisting Humberside Police, in 2018.
They have also undertaken several other trials in and around London since then.
South Wales Police piloted the technology during the week of the 2017 Champions League final in Cardiff, the first UK force to use it at a large sporting event.
Facial recognition has also been used at a number of privately-owned UK sites, including in shopping centres, museums and conference centres, according to an investigation by civil liberties group Big Brother Watch.
– Why is it controversial?
Campaigners say facial recognition breaches citizens’ human rights.
Liberty has said scanning and storing biometric data ‘as we go about our lives is a gross violation of privacy’.
Big Brother Watch says ‘the notion of live facial recognition turning citizens into walking ID cards is chilling’.