The KidReadler 1.6 supports custom backgrounds to be used, there are two requirements – files should be named as irbg. and to be downloaded in regular way (stored in Downloads directory).
Many images are royalty-free licensed, available for personal and commercial use. If you are an author, can prove it and do not willing to see your images here just let us know. Other are commercial licensed by pngtree or similar.
Just click image to download it.