A supermarket store has installed face recognition cameras to stop children buying alcohol and cigarettes.
It is thought to be the first time a UK retailer has used the technology to identify underage customers.
The scheme is being piloted at an undisclosed branch of Budgens in London, where cameras have been installed in each of three checkout lanes.
Charlie Willetts, managing director of Charton Ltd, which is supplying the software, said "a number'' of supermarkets and convenience stores were interested in using the technology to create a database of customers.
The cameras monitor customers as they approach the tills, transmitting information to a control centre in Worcester.
The customers' facial features are automatically scanned against a database of images of young people who have visited the store before.
If the system recognises someone who has previously been unable to prove they are 18, a signal alerts the cashier who will refuse to serve them.
The system also identifies when a customer has previously verified that they are 18 or over, enabling the sale to proceed more quickly.
Young customers who are not recognised by the system will be asked by the cashier to provide proof of their age when buying drink or cigarettes and their details added to the database.
Facial recognition software identifies individuals by taking measurements between key points on the face.
Mr Willetts said information about 1,500 individuals was currently stored on the computer, which had the capacity for almost two million.
However a number of technical issues and compliance with data protection laws needed to be resolved first, he said.
Face recognition technology is increasingly used by police and other law enforcement agencies to match CCTV footage of suspects with images of known offenders.