The periphery of a Taylor Swift concert is as thought out as the show she presents on stage. Beyond the traditional merchandise stands, there are often dedicated selfie-staging points and staff distributing light-up bracelets. When Swift performed at the Los Angeles Rose Bowl venue on 18 May, fans could watch rehearsal clips at a special kiosk.

What they didn’t know was that a facial recognition camera inside the structure was taking their photographs and cross-referencing the images with a database held in Nashville of hundreds of Swift’s known stalkers, according to a Rolling Stone report.

Mike Downing, chief security officer of Oak View Group, an advisory board for venues including Madison Square Garden and LA’s Forum, told Rolling Stone: “Everybody who went by would stop and stare at it, and the software would start working.” Downing had been invited to witness a demonstration of the system as a guest of its manufacturers.

While some have raised privacy concerns over the ownership and storage of the images, concerts are technically private events, and Swift has no obligation to notify ticket holders that they may be surveilled. The Guardian has contacted Swift’s representatives for comment.

Swift has a number of known stalkers. In September, she got a restraining order against Eric Swarbrick, who had been harassing her with letters threatening rape and murder since September 2016. In April, 38-year-old Julius Sandrock was arrested outside her Beverly Hills home. He was wearing a mask and had a knife in his car, and told police that he had driven from Colorado to visit the singer. Swift took out a restraining order against him in May.

Also in May, Mohammed Jaffar was sentenced to six months in jail and five years’ probation having been convicted for burglary after he appeared at Swift’s New York home five times in two months.

The use of facial recognition software is rising at public events. Ticketmaster has invested in startup Blink Identity, which aims to move fans through entry points more efficiently and combat touting. Israeli artificial intelligence company AnyVision said it was working with an undisclosed London arena to reduce bottlenecks at turnstiles.

In April, Chinese police used the technology to arrest a man attending a Jacky Cheung concert in Nanchang. The 31-year-old, who was wanted for “economic crimes”, was located among a crowd of 60,000 concert goers.

A recent UN report criticised the use of facial recognition by police in south Wales during a peaceful demonstration as disproportionate and unnecessary. Liberty and Big Brother Watch have backed two legal challenges against police forces in south Wales and London over their use of automated facial recognition.