Microsoft has launched a free online tool to help try and prevent the spread of child sexual abuse images.

According to Microsoft, around 720,000 illegal images of children are among the 1.8 billion photos uploaded to the internet every day. PhotoDNA is a free cloud-based service that can be used to hunt down and remove these photos from the web. "Finding these known child sex abuse images in that huge universe is like finding a needle in a haystack," said Courtney Gregoire, a senior attorney at Microsoft's Digital Crimes Unit. "We needed an easier, more scalable way to identify and detect these worst of the worst images ... and that's how the concept for PhotoDNA in the cloud was born."

The tool has been designed to be used by companies like Flipboard, which allows users to share content, the ability to identify and halt the spread of these images in order to prevent young victims and ensure the platform remains safe. "The Flipboard community is built on the desire to inspire each other with the things we love. Our community needs to trust that we do everything possible to stop the spread of illegal content, especially images of child sexual abuse," said David Creemer, Flipboard's head of platform engineering. "Manually searching for a handful of illegal images among the millions uploaded and curated every day is simply an impossible task, so we looked for a solution and found it in Microsoft's PhotoDNA. Together we built an effective service that scales and works great."


Flipboard, along with the likes of Twitter and Facebook, have been using the service for some time, but by placing the tool in the cloud Microsoft is making it available to smaller companies and other organisations that might want to allow users to upload content, but want to ensure that this content is of a legal nature. "The fact that the service is free and in the cloud completely eliminates a financial and budgeting hurdle that might otherwise stand in the way of service adoption," says Mike McCarter, Microsoft's director of online operations.

The tool has been constantly evolving since it was first developed in 2009. It was tackling the problem of the wide circulation of photos of abuse victims, which would crop up repeatedly in different locations across the internet. It was adapted to ensure that it would be able to recognise these photos even if they had been slightly altered or marked -- common tactics for attempting to fool the software.

PhotoDNA has been trained to convert every image it encounters into grayscale, before creating a grid across the image and assigning a numerical value to each square of that grid. The numerical values are combined to create a unique image signature. PhotoDNA will then be able to identify exploitative imagery whenever it comes across any photo with a signature matching one held in its database of known illegal images. This means that images don't need to be scanned or looked at in order to for their content to be declared illegal.


Of course, from time to time there is a need for imagery to be manually reviewed. Chat network Kik is one service that uses PhotoDNA and relies heavily on the automated policing of the images uploaded by its 200 million global users, but also must rely on some human moderation.

Kik's head of privacy, Heather Galt, has praised the tool however saying that not only has it helped the company identify and remove illegal content but that it is "so fast and does its work so efficiently that it’s been implemented with no negative impact whatsoever on the experience for users".

Now it is in the cloud, PhotoDNA should be quicker still. McCarter claims that the combined speed and efficiency of Microsoft Azure and the enhanced algorithm means that the tool should be 1,000 times faster at identifying imagery than previous versions.