Facial recognition is again in the news, after Information Commissioner, Elizabeth Denham, blogged about her concerns. However, many of the news stories and comments on social media highlight that there is very little understanding of the fundamental problems surrounding police use of this technology.

In very simple terms, facial recognition systems work like a game of snap - matching two faces together and then telling an operator that it has done so. To make the software work, the police need a suspect image and a database with which to compare that suspect image.

However, the problem isn't the software, how it works, or its success or failure to catch criminals. The real problem, and where the debate should be, is around the police databases that are being used to find a match.


Police retention of custody images

If you’ve ever been arrested, you’ll know how the system works. You’re taken to a police station, ‘booked in’ to a custody suite and given your rights and entitlements to legal advice - and here’s the important part – at this point you are told that you will have your fingerprints, DNA and photograph taken - this is all before anything else happens, before you’ve spoken to a solicitor, been questioned, or anything. Simply being arrested and taken to a police station means that the police will automatically take fingerprints, DNA and photographs - what we now call ‘biometrics’.

Once upon a time, these things would only have been taken from you if you were charged with or cautioned for a crime. However, in the early noughties, legislative changes meant that anyone arrested and taken to a police station had their biometrics taken. More than that, it meant that these things could be retained forever, regardless as to the outcome of the case, regardless of whether you were ever charged with a crime or cautioned.


Arrest is sometimes used as an administrative process by the police, it is by no means a finding of guilt and absolutely no inference can or should be drawn from the fact that someone has been arrested. The obtaining of ones biometrics at the point of arrest then, and these then being retained forever, in instances of zero conviction or guilt, seems rather unfair?

As a result of this grey area, there were a number of court challenges during the mid-2000s about whether or not this practice was right, or indeed fair.

In 2012, the government changed the legislation governing the retention of these biometrics, and the Protection of Freedoms Act was introduced. The act brought in legislation which said that innocent people, who have never been cautioned or convicted of a crime, should not have their fingerprints, or their DNA retained indefinitely following any arrest, and that it should be deleted if they were not charged or cautioned.


However, custody images, the photographs taken of you as you arrived at the police station after arrest, also known as ‘mugshots’, were left out of the legislation. This was because the High Court ruled, in 2012, just as the Protection of Freedom Act was being introduced, that the police policy on retaining images of unconvicted individuals breached human rights laws. So the government didn’t feel that photos needed to be part of the Protection of Freedoms Act. as their retention was already ruled as illegal, and therefore there was no reason for introducing further legislation.


Police heads in sand

The police were told to delete the ‘unconvicted photos’. But there was a problem. There were tens of millions of images, and the police had no easy way of identifying ‘convicted photos’ from ‘unconvicted photos’. So, in good old fashioned police style, they buried their heads in the sand and did nothing.

By 2017, five years after being told that it was illegal to retain unconvicted photos, little had been done to weed out innocent people from police systems.  The government, beginning to lose patience, told police forces that it was now taking too long, that they had to delete images on request.


But this was no overarching solution and the matter has since been repeatedly raised in both Houses of Parliament, and by the Information Commissioner.  

While the police themselves are officially saying that facial recognition is not being used against these illegally retained custody photos, evidence very much suggests otherwise.

According to NEC, the IT company which announced in July 2017 that it was to enter into a scheme to supply and trial a facial recognition system with South Wales Police - their system will be: “used to cross-check still images and recorded video taken at crime scenes against approximately 500,000 photos currently held in its [South Wales Police’s] custody image database.”


And South Wales Police themselves offered a degree of support that they had, and indeed were, using the NEC software against the custody image database, with Inspector Scott Lloyd telling Wales Online: “...we’ve got the ability to take that probe image and cross map it against the 500,000 custody images we have as an organisation.”

Whatever the actual truth is, it is the illegal retention of images that remains chief among the reasons why there is so much hostility to something which would ultimately help in the fight against crime.

There were already huge legal ramifications surrounding the police’s current illegal retention of innocent citizens’ images, but by introducing facial recognition technology into the mix, we also encounter the possibility of these innocent citizens being on the underlying databases that are employed to produce a match.

But surely it's not that difficult to remove images of those people not convicted of a crime?

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Well actually, it’s a huge problem, and here’s why:

Custody images are taken as soon as you arrive at the police station, and are referenced by your name, and custody number. The Police National Computer is what police use to track your arrest and conviction history through the criminal justice system.. But this is an entirely separate system to that which holds the photos. So your photo sits entirely on its own with no indication as to whether you are innocent or guilty of the matter you were arrested for.

To check that a photo of a person is ‘convicted’ or ‘unconvicted’, requires a police officer to check the date and location the photo was taken, and marry this up against what’s known as an Arrest Summons number on the Police National Computer.  They then have to follow the Arrest Summons number to see if the arrest led to a conviction. To cut a long story short, that’s likely to take an officer several minutes per photo. Fingerprints and DNA profiles, are much easier to trace, they are eventually married up, and populated with the AS number, so locating ‘unconvicted’ biometrics of this type is much easier.


All of this procrastination by the police is holding up the development and use of newer facial recognition technology, technology that will keep us safer in the long run. Why don’t they just get on with deleting the photos of unconvicted people? The longer it goes on, the longer it’s going to take?

The reason is because we are approaching 21 million images in total on the police databases. It would take a full-time team of 1,000 people more than 18 months, working flat out, just to clear what's already on there. It’s the cost, that’s why they are procrastinating.


The police needs to rethink how they are storing and retaining these photos. They need a new system, a way of tracking the photos via the Arrest Summons number, as this is where the problem starts. Once that new system is in place - they are going to have to bite the bullet and forget everything that they have ever collected, and delete the entire store of images - or spend the money, time and effort to go through what they hold and sort out the problem image by image.

But those decisions need to be made now, not next year.

Every hour of every day, more photos are collected.

Every month, the use of facial recognition software by the police increases.

This thorny issue is only going to cost more to put right in the long run - and become increasingly fraught with legal difficulties, if we refuse to confront it now.  

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To find out what information the police hold on the Police National Computer (PNC) about you, visit:

You can request that your PNC record, fingerprints and DNA be deleted here if you have been arrested and never charged:

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You have the right to have your custody photos deleted if you were arrested and not convicted/cautioned. Request so in writing to the chief officer in charge of the force area where you were arrested.

David Videcette is a former Scotland Yard detective specialising in counter-terror and organised crime. He is the author of The Theseus Paradox and The Detriment based on real events.