In a new report, Commissioner Dr Brian Plastow said a “sizeable proportion” of custody images taken between 2019 and 2024 are of such low quality they are unsuitable for police use in relation to facial searching technology.

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.

The quality and resolution of any image uploaded can significantly impact the effectiveness of such retrospective facial searches. Now a joint report from The Scottish Biometrics Commissioner and His Majesty’s Inspectorate of Constabulary in Scotland has called on Police Scotland to improve the resolution of its custody images.

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 states Police Scotland 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 within the PND for facial searching purposes.

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.

“Police Scotland should ensure this issue is solved, particularly considering the adoption of new systems such as the UK Home Office Strategic Facial Matching Project.”

The report states the use of RIST is both lawful and ethical in Scotland – and that Police Scotland has never used live facial recognition technology. It notes Police Scotland uses RIST via two databases – the Police National Database and the Child Abuse Image Database (CAID).

CAID is a UK policing database which uses facial matching technology to identify both victims and perpetrators of online child sexual abuse. Police Scotland carried out 3,813 facial searches via the PND between April 2023 and March 2024 – and 193 searches via the CAID.

For comparison, the Metropolitan Police carried out 31,078 and Greater Manchester Police carried out 5,290 searches via PND over the same period.

Figures obtained from Police Scotland revealed that when it had carried out a retrospective image search, a potential match was found in just two per cent of cases.

Dr Plastow said: “The overall quantitative contribution of retrospective image search technology to policing is very low – the vast majority of crimes reported to the police in Scotland do not have an image obtained during the enquiry investigation.

“But it can have a high qualitative value when dealing with some serious crime types.”

The report made four recommendations to Police Scotland.

It said Scotland’s national police force should develop a bespoke policy on the use of retrospective image search technologies, and that it should conduct a training needs analysis for all officer and staff regularly working in this area. It also said Police Scotland should improve the collection of data evaluating the effectiveness of such technologies and do more to promote public understanding of its value.