Creating backgrounds(BGs) is definitely different on how you create sprites or cutscenes. Furthermore, you can reuse them on your future projects or at least render them. There's a lot in the internet that you can possibly use (remember to credit the one who made it) though sometimes it just doesn't fit the style of the overall theme of your visual novel. The following are great sites to rummage through:
deviantART[dee·vee·un'nt·ART] is the world's largest online art community where artists and art enthusiasts can share their work. I decided to just post my progress in digital arts here in my deviantART page. Feel free to check it out and if you liked something, don't forget to add it to your favorites. Oh, here's one I haven't submitted yet:
Miss Universe 2007 - Philippines costume
This sketch was a request from a friend of mine. I may try to outline it in the future.