PhotoDNA is an image-identification technology used for detecting child pornography and other illegal content which is reported to the National Center for Missing & Exploited Children (NCMEC) as required by law. It was developed by Microsoft Research and Hany Farid, professor at Dartmouth College, beginning in 2009. From a database of known illegal images and video files, it creates unique hashes to represent each image, which can then be used to identify other instances of those images.