My rules are VERY simple:
1- You do NOT have to request permission to use my piece for any non-commercial purposes. I WOULD like a link in either comment or note to the finished work though, mostly because I'm interested in seeing the variety of things people come up with.
2- If you intend to profit by use of my work, it must be significantly altered so as to be it's own work of art and not just a reprinting of my photo. If my photo happens to be a focal point of the work, credit would be nice If you have a commercial use for my photo AS IS, please content me about compensating me for use (a girl can dream, right?).
3- My photos of children are NOT to be used in any pornographic or sexually insinuating artwork. Photos of myself or my knotworks are okay for use in more mature extrapolations, as long as they remain in good taste and I see the final result (I am pretty open-minded, so I don't see there being any problems). I will indicate on photos of other people whether or not they are available for "mature content" works.
That is all- have fun creating!!