Lists of hashes help the sorting process but their usefulness is limited by the changes regularly made to images.
An image-processing tool that can ignore those tiny changes and work out what other images it resembles has been developed by Microsoft researchers.
Instead of a hash, this creates what its creators call a
signature for each image. Unlike a hash this signature does not change when an image is altered or manipulated.
No matter how much it’s changed, the underlying properties of the image’s signature remain the same, said Stuart Aston, chief security officer at Microsoft UK.
Called PhotoDNA, the tool was developed to keep an eye on images uploaded to other Microsoft services and Facebook and now, with the help of Swedish firm NetClean, is being given to police forces to help them categorise images — via redwolf.newsvine.com