http://en.wikipedia.org/wiki/Affirmative_defense

The term means that such a defense will not be immediately declared invalid, not that it will necessarily work.  Although yes, seeing a lawyer is probably not a bad idea if you're interested in pushing the envelope.

Another big item is Title 18 §1466a:
http://www.law.cornell.edu/uscode/18/usc_sec_18_00001466---A000-.html

This section is the newest part, and since it manages to abstract "minor" and "real human being" from the segment of obscenity law, imo it is pretty important to take a look at also.  Probably it would have made more sense if I'd cited this piece first, sorry.  Most specifically:

> Quote - (c) Nonrequired Element of Offense.— It is not a required element of any offense under this section that the minor depicted actually exist.

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