Faces of revellers at a weekend music festival were scanned by police so that they could be compared with a European criminal database.
Facial recognition cameras were placed at different locations around the Download festival, in Donington Park, to capture the faces of the 90,000 people who attended.
In the first trial of such technology being used outside, the images were compared to a database of custody images kept by Europol.
Detective Constable Kevin Walker, of Leicestershire police, told the website Police Oracle that it was intended to uncover organised criminals who steal mobile phones at music festivals.
However, the move raised concerns about privacy after it emerged that other forces might use the technology at their summer events, if the trial proves successful.
Mr Walker told Police Oracle: “It is one of the first times it has been trialled outside; normally it is done in a controlled environment. There has also been a lot of interest from other festivals and they are saying: ‘If it works, can we borrow it?’ ”
Privacy campaigners expressed concern that the rights of innocent revellers were being infringed as their faces were being scanned, potentially without their knowledge.
Renate Samson, of Big Brother Watch, a campaign group against increased levels of surveillance in the UK, told Vice.com: “It’s one thing to pay good money to think you’re going to enjoy yourself at a festival. To then unknowingly find that your face is being scanned using biometric technology and compared with a database of people in custody from across Europe takes the edge off the fun.’
Leicestershire had some of the highest numbers of CCTV cameras in the UK between 2009 and 2011, she added.
Crime at the Download festival dropped to only 91 incidents last year, compared with 327 in 2007.
Leicestershire police said that the images of attendees would be destroyed by the middle of next week.
A spokeswoman said: “Having your picture taken at Download is a condition of entry and is stated on every ticket. There are a number of tactics the police use to identify criminal activity and they do this to keep people safe and ensure that those who have come to the festival to enjoy the music, can do so without becoming a victim of crime.”