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Police in London are testing facial recognition software on Christmas shoppers, hoping the technology will detect known and wanted criminals in the crowds.

According to The Verge—a website that reports on cutting edge technology—this week's experiment is the seventh time the Metropolitan Police Department has tested facial recognition in public. The technology has previously been used at large events, including the Notting Hill Carnival in 2016 and 2017, and Remembrance Day services last year.

The Verge reports that the cameras will be attached to lampposts or mounted on vehicles. The department is using software developed by Japanese firm NEC that measures different facial features such as the distance between the eyes and the length and angle of the nose. The scan is then compared to a database of police mugshots.

Critics of the technology have said that it is not yet advanced enough to be trusted for accuracy, noting that "false positives" can result from a variety of factors such as poor lighting.