I'm sure you've all seen the news last week about a model who was busted posing nude for a photographer in the Metropolitan Musem. Leaving aside the issue of whether photography on specifically the Museum's property is legal or not, the fact is that nude public photography in public streets in New York is perfectly legal. The "indecent exposure" law specifically makes an exception for plays, performances etc. and this has been held to apply to photography too. Read all about it here