The Trace portraits—which include Nelson Mandela, Edward Snowden, and the Tibetan pop singer Lolo—were laid out in the artist's studio in Beijing prior to being sent to Alcatraz.  Photo 1 of 6 in Ai Weiwei Exhibition Takes Over Alcatraz by Erika Heet

Ai Weiwei Exhibition Takes Over Alcatraz

1 of 6

The Trace portraits—which include Nelson Mandela, Edward Snowden, and the Tibetan pop singer Lolo—were laid out in the artist's studio in Beijing prior to being sent to Alcatraz.