PhotoDNA scans images for child abuse (2009)

Posting this in antique article in context of the new Facebook 'intimate images' tool because it talks about an academic study of the false positive rate in a similar tool:

" In the latest announcement, a large scale test of the PhotoDNA tool found that less than one false positive occurred in every billion images scanned, said Hany Farid, a professor of computer science at Dartmouth and co-developer of PhotoDNA. In addition, the software recognizes about 98 percent of images derived from those in its database.

"We tested it over billions and billions of images," he said. "We tried very hard to make it very efficient ... and to minimize the false alarm rate.""