Well reading the Us guidelines as it says it's one of many. but it will also say if you make a collage out of many little parts like cutouts of journals the collage will be protected as the new creation has enough originality, in theory one will take a purchased 3D convert it take parts off and rebuild it new then at this point it is new and belongs to the new creator that put in enough originality as said else the world would have to accuse every painter that made a portrait , accuse every photography of private houses or people that did not agree to have a picture taken from. well in theory we would have to pay for every picture taken and any can accuse the other of Piracy. it seems to be is the US law. So in theory if taking a Texture you pay for it to one who took the picture or take it your self but are you certain that the one who took the Picture paid the one who owned the wall ? or did you tell the one that you have taken the picture from that you will earn with it ? in a case of skin textures Models are very expensive it would never cover the income of a 3D doll sold in the store so in theory to release a character ad-don for a Doll the creator would need the proof and have the model's agreement to have used hes skin.