Hany Farid wants to clean up the Internet. The chair of Dartmouth’s computer science department, he’s a leader in the field of digital forensics. His hallmark project is PhotoDNA, which detects child pornography as the images are posted online. Now Farid is taking the same model of PhotoDNA and doubling down: he wants to find and root out extremist content that supports real-world violence and terrorism. “If we want to really prevent extremist content from getting online in the first place, we need to develop a technology to process billions of images and videos daily,” he says.

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