It's important that artists who create
premade backgrounds properly credit the resources used, and important that artists who use
premade backgrounds make sure they're only using works with valid stock/resources. This may seem confusing or like a pain in the a** right now, but in the long run it's for your protection against possible (unintentional) copyright infringement. Hope this helps you understand!
Screenshot is of a premade background by *B-r-a-c-i-a-t-a
Also see this excellent article by =CelticStrm-Stock [link]
for more information on the rules regarding premade backgrounds.