They are the faces of real people, portrait-like sculptures etched from an almost powdery substance. The eye colors are distinct, the facial contours sharp, even though the artist, Heather Dewey-Hagborg, has never met or seen her subjects.

Instead of using photographs or an art model for her work, Ms. Dewey-Hagborg scoops detritus from New York City's streets—cigarette butts, hair follicles, gum wrappers—and analyzes the genetic material people leave behind. Ms. Dewey-Hagborg, a Ph.D. student in electronic arts, makes the...