Well, I'd be fine with you using the image as long as you don't claim that it's your own, I suppose. I updated the creative commons copyright license on the black-backed flag, and I'll be sure to do the same with the others.
The thing about the flag there, though, is it contains some very specific references to my own works, which would probably not really make much sense with your group. Obviously, they aren't explicitly mentioned in any non-made-up language, but it's supposed to represent a fictional star-chart and rings of influence for the central planets noted - but again, use it if you wish to - someone else tattooed it on their body.
I've never used Second Life, personally, but I might check it out. Hell, fictional though they may be, I may even have some input that could be interesting for you and your friends. I'll take it on your word that the image isn't going to be used in any depraved sort of manner, but may check it out anyway. We should move any further contact to private messages, however.