Facial recognition technology is increasingly widespread. You might use it to unlock your phone or computer. It’s used in airports around the world and some shops are using the software to catch or deter shoplifters. Now it’s being used by the police in two parts of the UK. The Metropolitan Police is using live facial recognition cameras on London streets and it’s also being used by police in South Wales. The technology means that faces captured by the cameras can be checked in real time against a watch lists of suspects. But creating a face print or facial signature for everyone who passes a camera is controversial. Privacy campaigners say the technology is often inaccurate and infringes on an individual's right to privacy. The police argue that privacy concerns over the cameras are outweighed by the need to protect the public. We speak to the BBC’s Home affairs correspondent, Danny Shaw about why the police want to adopt the technology. We also find out how the technology works with Maryam Ahmed, who works in the BBC’s data journalism team and has a PhD in machine learning for image analysis. Presenter: Matthew Price Producers: Katie Gunning and Alicia Burrell Mixed by Emma Crowe Editor: Philly Beaumont