A million images of child sexual abuse have been “digitally fingerprinted” as part of a drive to prevent this material from circulating online.

British non-profit organisation the Internet Watch Foundation (IWF) says it created the digital fingerprints – known as hashes – for pictures taken from the UK government’s Child Abuse Image Database.

These hashes act as unique digital codes which are shared with law enforcement and service providers to flag and block any attempts to share or distribute this material online.

IWF, which works to identify and remove online child sexual abuse imagery, adds them to its Hash List, which can then be referred to by tech companies to block or remove such images from their networks.

The images assessed and hashed by the IWF include some of the most extreme examples of child sexual abuse material, known as category A and B material.

Some of this material is so extreme that the IWF taskforce members are only allowed to work four-hour shifts, taking regular breaks, and with access to the best counselling and support, IWF CEO Susie Hargreaves said in a statement.

The organisation also has a tool that allows these hashes to be enriched with additional contextual metadata that explains the exact nature of the abuse taking place to the child.

“I have three children 11 and under. The job has changed the way I think about them and the internet,” an IWF assessor, identified only as Beth, said in the statement, adding some of the material processed featured children as young as five years old.

Last month, the European Commission put forward new EU legislation that would force internet service providers to detect, report and remove child sex abuse content. It said the current system based on voluntary detection and reporting was “insufficient to adequately protect children”.

Some 85 million pictures and videos depicting child sexual abuse were reported worldwide last year alone, and many more are going unreported, according to the Commission.

In 2021, the IWF took action to remove a record 252,000 URLs that it confirmed contained images or videos of children being raped and/or suffering sexual abuse.

“The sexual abuse and exploitation of children is one of the most appalling and distressing crimes, and we are doing everything to prevent and pursue offenders,” IWF Safeguarding Minister Rachel Maclean said.