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:<p>" 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.<p>"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.""