For the first time in 25 years, an American photographer known for inspiring massive groups of people to pose nude in public spaces is capturing his subjects apart, in their homes, and sometimes wearing a single article of clothing: a mask. Every year, Tunick organizes at least one group nude shot with hundreds — sometimes thousands — of volunteers. Last year, it was in front of Facebook's Manhattan headquarters , where more than people — mostly women — donned their birthday suits and held images of nipples to protest the social media giant's use of censorship. In other years, he's choreographed a sea of flesh outside the Sydney Opera House in Australia, and inspired 18, people to strip down in Mexico City's Zocalo square. The photo shoots usually highlight a social, political or environmental concern, using the human body as an art form.