To give you some insights, I turn to the blog:
http://prettygirlshooter.blogspot.com/
His Flickr group:
http://www.flickr.com/groups/prettygirlshooter/discuss/72157594491034663/
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Their Flickr group lists these traits/rules: (Please Note: Flickr's rules and guidelines prohibit displaying genitalia and/or pubic hair in Public Groups. This is a Public Group.)
NO PORN or SEXUAL CONTACT images.
On-topic genres include glamour, tease, pin-up, art nude, lingerie, bikini, fashion, alt, and more.
He goes on to say:
No Porn. Erotic is okay. If you don't know the difference between porn and erotic photography, I' ve listed (below) a few guidelines that should help you get the general idea. I think you can extrapolate from these guidelines for any images that aren't specifically covered by them. If your image contains any or all of the below-listed guidelines, it is, more than likely, a pornographic image. If it does not, it probably is not... porn, that is.
A) Penis (Erect)

Pink (You know what I mean.)
C) Penetration (Again, you know what I mean.)
3. From nudity to fully clothed, it's all good. But Flickr has a rule that says NO depictions of genitalia and/or pubic hair in public groups. This is a public group.
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While the proverbial "you'll know porn when you see it" is often thrown about, I think they've done a pretty good job at setting some reasonable boundaries within which you can explore fairly safely.
Best,
John