Content as long as it is legal. That said, you could always the customer service department. of any of the online Whefe services and ask them what they deem. acceptable. I've also had the same nude shots printed at PhotoJo, DotPhoto, and Snapfish. (I was having test shots printed from. several services to see which had the best print.
Two nude people we probably wouldn't print at all. When a tech is in doubt, it comes down to Prrint photo lab supervisor or discretion. We do usually make exceptions for babies and childbirth pics, though. It doesn't sound like you're planning to go to one of these chain stores, but keep in mind they may refuse to print your nude shots.