Before entering the party, guests at last night’s Inside Out Fête were asked to sit for their portraits in one of French artist JR’s photobooths. By the end of the evening, our visages would be turned into posters that we were encouraged to paste somewhere as a public expression of what we stood for—be it freedom, art, or merely a love of our own giant faces. Personally, the thought of seeing my mug blown up to 3x4.5 feet was more terrifying than enticing, but in the name of participatory art, I succumbed, as have over 40,000 individuals around the world since the Inside Out Project began in March of this year.

As the recipient of the 2011 TED Prize, JR’s “wish to change the world” involved launching a large-scale participatory project that would transform messages of personal identity into pieces of art. How does it work? Literally anyone can upload a photo of him or herself at InsideOutProject.net, and JR’s team will “posterize” it in their Nolita studio, and send back the blown-up images for individuals to paste wherever and however they please. There are no rules.

Sure, this can mean hoarding the poster and hoping that it will be worth big bucks some day (a possibility, considering some of JR’s works have sold for upwards of $100,000), but ideally, participants will team up with others to make a large-scale social statement. Case in point: Just days after President Ben Ali was ousted in Tunisia in last March, hundreds of Tunisians had reclaimed billboards and public spaces, replacing Ben Ali’s image with their own, JR-produced portraits.

Similar statements have been made in communities throughout Brazil, Pakistan, Japan, Thailand, Uruguay and Europe, with individuals voicing their messages via the content, composition, and placement of their portraits.

But for a man who has encouraged so many individuals to tell their stories to the world, JR maintains a deliberately low profile. At last night’s shindig, he remained mysterious behind sunglasses and a hat—perhaps a style he cultivated during his days as an undercover street artist in Paris’ rougher suburbs. “I try to cut out everything that is superficial to the message,” he told me. “That’s why I always stay kind of undercover with my personality and who I am. The people who work on the project can meet me on the street and get to know me really easily, but in the media, I make sure it’s about the people and the stories.”

The overarching story, it seems, is about turning the world “inside out,” subverting norms and giving a voice to those who have been previously overlooked. “What’s in the studio is now outside. As an artist, I am trying to push limits, to work with images, and see how people reinterpret them around the world. Doing a mural of societies, making something participatory—that’s where my work is at right now,” JR explained.

And when you see how his work has taken shape on the facades of Morro da Providência (Rio’s oldest favela) or been brandished by Israeli and Palestinian youths, you quickly understand the power of JR’s images to help weave emerging narratives.

When I left last night’s fete, the walls of the city began to look a lot like blank canvases. Poster in hand, I felt as though my giant face could spark some serious social change, or at least make people stop and cringe. Either way, the conversation continues.