"Everyone who does development for large touch screens knows that [user differentiation] is a problem," says Daniel Wigdor, a professor of computer science at the University of Toronto. Wigdor was not involved in the research. "Bootstrapper's technique is elegant because it's all contained in a particular box," he says, referring to the prototype's housing for the cameras and lights.

Still, Bootstrapper isn't perfect. Baudisch notes that if a person contorts his or her arm in a way that makes it appear to align with someone else's feet, the system might mismatch a user with a gesture. The current system also requires that at least one foot maintain direct contact with the floor. And if different users wear the same type of shoe, as they would if in the military, for instance, the system's main function is rendered useless.

The best way to identify users around a touch table is probably to combine several approaches, says Wigdor. For instance, a Bootstrapper-like system could be paired with sensors in a chair. "I can see it as one of three or four techniques," he says.

Baudisch thinks elements of Bootstrapper could find a home in open spaces like department stores. Cameras could track whether a person paused at the sweaters or purses, for example, and then suggest a sale via a digital advertisement.