Last year, Steven Livingston, professor of political communication at George Washington University, astonished attendees at a conference on the geopolitical pros and cons of satellite imagery. He didn't produce evidence of new military mobilizations or global pandemics. Instead, he showed a video of figure skater Katarina Witt during a 1998 skating competition.

In the clip, Witt gracefully plies the ice for about 20 seconds. Then came what is perhaps one of the most unusual sports replays ever seen. The background was the same, the camera movements were the same. In fact, the image was identical to the original in all ways except for a rather important one: Witt had disappeared, along with all signs of her, such as shadows or plumes of ice flying from her skates. In their place was exactly what you would expect if Witt had never been there to begin with-the ice, the walls of the rink and the crowd.