. A record 18,000 people took off their clothes to pose for U.S. photographic artist Spencer Tunick on Sunday in Mexico City's Zocalo square, the heart of the ancient Aztec empire. Tunick, who has raised eyebrows by staging mass nude photo shoots in cities from Dusseldorf, Germany, to Caracas, smashed his previous record of 7,000 volunteers set in 2003 in Barcelona, Spain .