Perceptual hash functions are designed to return answers for images or sounds that a human might feel are similar. That is, small changes in the media don’t affect the output.

With a strong hash function it is almost impossible to reverse the hash value to its original content. The National Security Agency (NSA) designed the SHA-1 cryptographic hash function 10 years ago.

For more than six years, the SHA1 cryptographic hash function underpinning Internet security has been at death's door. Now it's officially dead, thanks to the submission of the first known ...