The “rapid” growth of a police facial recognition database could lead to innocent people being unfairly targeted, a watchdog has warned.
Biometrics Commissioner Paul Wiles said the Police National Database (PND) now had at least 19 million custody photographs on it.
However, it is thought that hundreds of thousands of these could be of innocent people.
The Home Office said police should delete images of unconvicted people.
In a government review published in February, the Home Office concluded that those who are not convicted should have the right to request that their custody image is deleted from all police databases.
A High Court ruling in 2012 said retaining the custody images of unconvicted people amounted to a breach of human rights.
The PND contains custody images, taken at police stations after someone is arrested.
Of these, more than 16 million have been enrolled in a gallery which can be searched using facial recognition software, including pictures of individuals who are released without charge or later cleared.
Mr Wiles pointed out in his annual report that facial imaging was also being used in public places, including to check Notting Hill carnival-goers against a watchlist.
“The use of facial images by the police has gone far beyond using them for custody purposes,” he said.
Mr Wiles, who has held the post since last year, warned wrongful allegations could occur from the “very rapid growth” of the database.
Currently, different forces use their own systems to upload images to the central database, with “varying degrees of image quality”, the report said.
“This situation could easily produce differential decision making and potentially runs the risk of false intelligence or wrongful allegations,” it added.
Mr Wiles, whose job is to scrutinise how police and other authorities retain information including DNA samples, profiles and fingerprints, said hundreds of thousands of people of innocent people were on the PND.
This is because they were later released or cleared in court, but never deleted form the database.
But Mr Wiles pointed out that police have the discretion to refuse such a request and warned that the “complex” proposals could result in a “postcode lottery”.
Renate Samson, chief executive of Big Brother Watch, welcomed the watchdog’s warnings, saying: “It is of very serious concern that the Home Office appear to be so unwaveringly set on embedding facial biometric recognition technology into policing without debate, regulation, legislation or independent scrutiny.”