Hypothetical legal question

Are there any lawyers here or anyone who knows law?
I was reading about the phenomenon known as sexting, which is described as pictures of people (generally minors) naked, partially nude, having sex, or in intimate or compromising situations sent to a spouse, lover, or significant other over a cell/video phone or an Internet connection.
I think legal definitions should be made before arrests, for instance the term intimate can mean sexual themes, but may be used for romantic and/or seductive situations.
Should a 16 year old wearing lingerie be considered illegal, I think not.

Would a picture of a naked minor in no sexual context be called child porn?
Could one be arrested for just possessing such a picture?
If a nudist family can get away with it, why can't the general public?