Poor quality custody photos could lead to crimes not being detected

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.

They say this must happen before Police Scotland can take part in any new facial matching services proposed for law enforcement purposes, including the potential use of live facial recognition technology

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 Scottish Biometrics Commissioner working jointly with HMICS on the detailed review, looked into areas including how often Police Scotland used retrospective image search technology (RIST) and their reasons for doing so.

Their 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 Service 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 gives examples of numerous cases where Police Scotland has used RIST successfully in the investigation of crimes and in the safeguarding of child victims.

One case involved a tourist who was sexually assaulted, by an unknown man who initially engaged her in conversation and requested her telephone number.

After he started sending her sexually offensive messages and images, Police Scotland successively matched the photo from his messaging app to an image obtained from a custody photo taken more than 20 years ago.

The man has been reported to the Crown Office and Procurator Fiscal Service for various sexual offences.

The valuable role such technology also plays as a welfare tool for police officers investigating cases of online child sexual abuse was also highlighted.

Dr Plastow said: “In the investigation of online child abuse the welfare of officers is an enormous consideration, as the scenes being viewed can be horrific and affect officers mentally over time.

“In one case we have detailed in our report, facial matching was invaluable in separating out footage of each child involved and vastly reducing the quantity of still images and hours of video footage to be viewed.

“It also provided reassurance that all the victims had been identified and safeguarded.”

The Commissioner’s report – a joint assurance review of the use of retrospective facial search technologies for criminal justice and police purposes in Scotland – 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.

Dr Plastow added: “In an increasingly digital world, the future of law enforcement lies in achieving the right balance between the introduction of new technologies for public safety and safeguarding fundamental rights.

“For biometrics, public confidence should be maintained with transparency, robust governance and independent oversight.

“This, along with the issues highlighted in our report, should prompt significant reflection for policing in Scotland.”