And better technology does not eliminate the need to decide what technology should never be allowed to do.… At 7:42 on a rainy Monday morning, Mei Tanaka stopped in front of the security gate of a newly renovated research facility. The gate had a camera mounted above it. A small screen displayed the familiar message: IDENTITY VERIFIED. Mei had seen systems like this before. At airports, office entrances, smartphone locks, and increasingly in public infrastructure, facial recognition had become almost invisible. The technology did not literally look only at a person’s eyes, nose, and mouth. It extracted mathematical features from an image—the relative positions of facial landmarks, contours, textures, proportions, and other patterns—and converted them into a numerical representation, often called an embedding, that could be compared with stored templates. But there was something else that interested Mei. She was a comput...