Latest technology combating child sexual abuse images online a “game-changer"

Published:  Mon 10 Aug 2015

Harriet Lester, IWF Technical Projects Officer

2014 was an extremely busy year for the Internet Watch Foundation (IWF). IWF Internet Content Analysts actioned 31,266 child sexual abuse URLs, an increase of 137% compared to 2013. Our team of analysts had almost doubled in size and unique abilities allowing us to pro-actively seek out illegal content meant we were removing more online child sexual abuse imagery than ever.

This year we are maintaining momentum and believe our latest announcement is a huge step forward in the fight against child sexual abuse imagery online. Our CEO, Susie Hargreaves, described it as a “game-changer”. The team and I have been working hard to provide a brand new service to the internet industry which will change how we find and remove criminal content forever – the IWF Hash List.

Developing the technology

Over the last 6 months, together with the internet industry and the Home Office, we have gone from planning a project around a potential IWF Hash List to having IWF licensed Members implementing it within their systems.

Looking back at the first meeting I had with industry where we discussed how we were going to make this happen, it was clear that implementing this as soon as possible was vital. We were developing a service from scratch, which would be a complex and challenging task, but we knew that this could revolutionise the way in which we fight online child sexual abuse material.

IWF analysts spent several weeks ‘hashing’ known child sexual abuse material. In simple terms a ‘hash’ is a digital fingerprint unique to an image which allows that image to be identified. Analysts would assess content to ensure it was illegal and then proceed to create a hash for the image. At the point of launching the hash list we already had a huge number of hashes created and ready for use. Analysts have been continuing to hash images on a daily basis from public reports, pro-active searching and external sources, meaning the hash list will continue to grow every day. The more child sexual abuse images our analysts find, the bigger the hash list grows and the more content we can prevent from being uploaded to the internet.

Implementing the list

In July, we were ready to begin using our new technology. We had created a list of known child sexual abuse material, ready to be implemented into industry services. The hash list got to work immediately. From day one of industry using the hash list, they were able to find and remove or block online child sexual abuse images sourced from our hash list.

We use various different hashes within our hash list. Microsoft’s PhotoDNA hashes are favoured among our Members because PhotoDNA hashes are able to identify images even if they have been altered.

We are aware though, that some companies may prefer to use different hashing methods. That’s why we are also offering alternative hashing methods. MD5 and SHA1hashes are cryptographic hashes, which will find exact matches of illegal images.

Thanks to our IWF Members

I would like to personally thank IWF Members Google, Microsoft, Twitter, Facebook and Yahoo for their help in making this project possible. We all believe that our shared vision of eliminating online child sexual abuse images is a huge step closer to being achieved with the introduction of this new technology.
Notes to editors:

Contact: Emma Hardy, IWF Director of External Relations +44 (0) 1223 203030 or +44 (0) 7929 553679.
About the IWF

The IWF is the Hotline to report:

·        child sexual abuse content hosted anywhere in the world;

·        criminally obscene adult content hosted in the UK;

·        non-photographic child sexual abuse images hosted in the UK.

For more information please visit
The IWF is part of the UK Safer Internet Centre, working with Childnet International and the South West Grid for Learning to promote the safe and responsible use of technology.

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