Fake videos have become such a potentially disruptive threat that the high-tech research arm of the Pentagon is launching a contest in early July aimed at detecting “deepfakes,” hoax videos so realistic that they could trigger political scandal or even spark violent conflict. Some 10 teams from major U.S. universities across the United States and Europe will compete in a two-week contest to devise techniques to distinguish between fake and real videos. “The goal is to provide the general public … a set of tools that we can use to verify images, video and audio,”said Siwei Lyu, a computer scientist...