Custody photos 'too poor' for facial recognition software

Custody photos can be used to detect potential matches from sources such as CCVT footage

Photos taken of suspects arrested in Scotland are often too low quality to be used by facial recognition technology, a report has confirmed.

The Scottish Biometrics Commissioner and His Majesty's Inspectorate of Constabulary in Scotland (HMICS) raised concerns about the quality of custody images being added to national databases.

Commissioner Dr Brian Plastow said a "sizeable proportion" of those taken between 2019 and 2024 are of such low quality they are unsuitable for software used across the UK to link suspects to other crimes.

Police Scotland said they were already aware of this issue and would consider recommendations in the report.

Police forces across the UK upload images of everyone they arrest to the Police National Database (PND), which allows officers to detect potential matches with photographs of suspects captured and uploaded from sources including video doorbells and CCTV.

The intelligence sharing system can lead to a person arrested for one crime being linked to numerous unsolved crimes.

While custody photographs remain mostly low-quality, Police Scotland will be unable to take part in new facial matching services, including the controversial live facial recognition technology.

MSPs have previously warned that using live facial recognition on members of the public would be a "radical departure from Police Scotland's fundamental principle of policing by consent."

But the report highlighted the problem with the current use of retrospective image search technology (RIST) when the custody images were not adequate.

Figures from Police Scotland revealed that a potential match was found in just 2% of RIST searches.

But it also gave examples of successes in Scotland including the sexual assault of a tourist who was then sent offensive messages and images from the perpetrator.

Officers matched the photo from his messaging app to a custody photo taken more than 20 years ago.

Facial recognition technology can also be used to compare images on the the Child Abuse Image Database (CAID) to identify victims and perpetrators of online child sexual abuse.

Suspects 'not being detected'

Dr Plastow said: "While carrying out this assurance review we were informed about the insufficient quality and resolution of Scottish images on the Police Scotland Criminal History System, which affects a portion of custody images captures between 2019-2024.

"This means a sizeable portion of custody images are not searchable under PND facial search functionality.

"This gap could mean that people who have had their custody image previously taken, are not being detected on future probe images uploaded by Police Scotland, which could lead to crimes not being detected."

The report stated that the force said a "software issue" was causing the custody images to be captured at a lower than recommended minimum size.

The images were then being additionally compressed using a technique that left them unsuitable for use with the PND.

Dr Plastow added: "Extreme caution must be exercised with any retrospective ICT fix to uncompress these images.

"If they cannot be fully restored to their original format, the reliability of the data could be significantly compromised."

Dr Plastow said there needed to be "transparency, robust governance and independent oversight" when using biometrics.

Assistant Chief Constable Steve Johnson said Police Scotland would consider the Scottish Biometrics Commissioner's recommendations in full.

"Our Biometrics Oversight Board is already aware of this issue and is overseeing work to improve the quality of images taken in custody and the collaboration with Home Office Strategic Facial Matcher Project, which mirrors the recommendations," he said.