The battle against child pornography is now being fought with new technology and the support of some of Silicon Valley's biggest companies. Facebook, Google, Microsoft, Yahoo, and Twitter are working with the UK's Internet Watch Foundation (IWF) to implement a new system that will help detect and block images of child pornography online.

IWF, a charitable foundation, has introduced a new technology that enables it to tag images of sexual abuse with distinct hashes — essentially codes that act like a digital fingerprint. The hash is generated by an algorithm; once assigned to an image, it's unique to it, making it easy to identify a specific image against a list of offending hashes. The IWF keeps a record of all the hashes, which it has only shared with the five tech companies so far, but plans to roll out to other IWF members soon.

Once the system is implemented, any image that is uploaded to Facebook, Twitter, or any other participating website is scanned. If the image has previously been tagged by the IWF, the system will detect its hash and automatically prevent it from being uploaded, and thus from being shared.

The IWF estimates that it can currently remove 500 web pages that contain child pornography per day, and that count will only increase as more images are identified and the hash list grows. But the technology does not as yet extend to the part of the internet where child pornography thrives: images shared anonymously over the darknet — peer-to-peer networks and Tor, for instance — are still out of reach. And while the hash list should help prevent certain images from being circulated on the more public web, the IWF says child pornography in video form cannot currently be hashed, either.

There is great potential here — as the hash list grows, it could conceivably hash millions of images and help block them. Google has long scanned the images that pass through Gmail for child pornography and had previously committed to working with the IWF, but there is no quick fix for a problem of this scale. However, the joint support of the tech giants should help widen the net.