When you choose background or model to use in your art, or purchase a product to transform into your proper creation, you gives attention to the use terms?
When you save a photograph stock inside of the DeviantART, for example, you must follow the rules that each stock possesss, so that one day does not come to have problems with copyrights, removal of its art or even though a process, that many times costs expensive. If you purchase a deep package of images in another site, you must read the rules of use, many you cannot be used to create other backgrounds for sale, others you only can be used for not commercial ends, others no have restriction. Take care with render stocks, when you purchase a product to poser or 3d, have a rule to be followed, if you render and save in png or jpg, you you can use it in the way that to want, safe some restrictions that each 3d creator possesss, you need trust in the stock of where load the image, to always keep a register of the name of the stock for future consultations, if possible, knows the name of who represents this stock. Some 3d creators, for example, do not allow that they create backgrounds for sale or distributed gratuitously, only allow the use in art of the proper purchaser. They exist stocks, out of deviantART, as SXU and Morguefile, that have general rules of use, and leave exempts some photographers to use requirements you add, as the personal use only, or to credit and to notify, in these case that, always takes care to also save the name of the photographer and the applicable rule the image. The use of a stock does not give to the right of property of the image, the author to it holds back the legitimate rights on it, not to be that you it buys this right. You have right as creative of the art and the person who supplied the resources so that it was possible, also has! If somebody says that it needs written authorization to use the stock, asked for the authorization and keeps in local insurance, is your guarantee! They are respected!

Thank you so much, hope your understand my bad english!!!