I look at it this way (as if anyone cared): Posting in the galleries here should mention/credit all people (paid or free) who helped make it happen. I see it this way because this is a community of artists. I think they should share just how they came about making their art. This serves 2 purposes in my HO: (1) If someone sees something that you used, they know where to get it. (2) It makes people whose items you have used, either purchased or taken freely, appreciate your credit. All-in-all, a friendlier place. But that is for R'City and its galleries. Should I ever sell an item (around the time hell freezes over), I wouldn't credit anyone. It wouldn't appear in the media it was presented, and the purchaser certainly wouldn't give a damn. The only thing I would ensure was that I sought (or had) appropriate rights to sell the item in question with concerns with whose items I used. In the background, though, I would certainly let the people who "assisted" know.