About five or six years ago, one of Karl Ricanek’s students showed him a video on YouTube. It was a time lapse of a person undergoing hormone replacement therapy, or HRT, in order to transition genders. “At the time, we were working on facial recognition,” Ricanek, a professor of computer science at the University of North Carolina at Wilmington, tells The Verge. He says he and his students were always trying to find ways to break the systems they worked on, and that this video seemed like a particularly tricky challenge. “We were like, ‘Wow there’s no way the current technology could recognize this person [after they transitioned].’”