
Quoting
Karen Kraft
It's tricky, as you probably have learned this summer. There are city ordinances, as well as county regulations, state laws, and national (federal) park, wilderness, and monument rules. Some activities are permitted only if they are non-commercial. That's the bad news. The good news is this: Almost all stewardship entities that oversee public properties have a public information officer (sometimes disguised as a "media contact"). They may have brochures, links to websites that explain the do's and don'ts, etc.
More importantly: NO NO NO! Do not "make sure" your nude or partially nude models are of legal age! "Making sure" will land you in a world of hurt. You need to document that fact in a rational way and preserve all of your records and documentation forever (as long as the publication, if any) is out in public -- on the Internet, that means forever.
Jotting down the name, date of birth and the drivers license number is insufficient. That is to say, it's just fine -- until it isn't. Then, he/she is long gone and you have a big problem. Ever see a fake I.D.? No? Go to any college town and you will find plenty of them floating around. And no, the fact that an underage person showed you a fake I.D. will not help your case in many jurisdictions. It's your duty to be sure.
Jurisdiction example: In California, we have miles and miles of beaches. The first 1,000 feet above average high tide is public, even if it's in front of someone's private beach/house. Then we have city parks that include beaches, county beaches, state parks, military bases, and so on.
Be honest: if you want to take nude photos as a hobby, say so. If you are engaging in a commercial venture, be right up front with that! The movie industry shoots nude or partially nude scenes at the beach all the time. They obtain a permit to do so and are subject to reasonable time, place, and manner restrictions (like production assistants providing a buffer between the public and the shoot).
You want to be cheap? Make arrangements with someone who lives at the beach and get their permission to shoot in front of their house. Trust me: that works great