Nude photographer
As long as you stay out of the no photography zone by the pool, you could hand your camera/phone to anyone and ask them to take a picture of you with all kinds of unique backgrounds. A good one might be from the beach at Mahogany Bay with the ship in the background. Just make sure nobody is in the background that hasn't given permission to be photographed. We handed our camera to someone and got a picture at the Garden of Eden nude rooftop bar in Key West last time we stopped there. That's another good one, since they have a spot just for taking pictures with a mural of the Garden of Eden in the background.
You also have the option of having the ship photographers take some professional ones (yes they will still take pictures of you when you are nude), but they run $15-25 each. I don't remember if any of them were on the beach at Mahogany Bay last year, but we did get one of us on the beach at Half Moon Cay with the ship in the background a couple of years ago. That one did have people in the water in the background, but since it was the ship's photographer there were no complaints.
On one of the subsequent trips to Half Moon Cay (we stoped there 3 years in a row) we got someone to take our picture in the water with the ship in the background, too. I agree that there are lots of great opportunities to get some good nude pics.