The hash they use is more complicated than that: converts images into a common black-and-white format and uniform size, then divides the image into square

The hash they use is more complicated than that: converts images into a common black-and-white format and uniform size, then divides the image into squares and assigns a numerical value that represents the unique shading found within each square. Together, those numerical values represent the "PhotoDNA signature" or "hash" of an image - https://www.microsoft.com/en-us/PhotoDNA/FAQ https://www.microsoft.com/en-us/PhotoDNA/FAQ What I was suggesting was that the hash generation tool they use be distributed so the hash can be generated locally before sending to MS. This way MS can continue to keep all known hashes to themselves while making it easier for businesses to bulk check images without huge bandwidth charges or privacy issues.