I don't know if anyone knows this but it's possible to change the background images on the Dingoo A-380.
To change them all you've got to do is make an 400 x 240 pixels BMP file and put it on the root of your external MicroSD card. I don't know if it works with the internal MicroSD. I didn't try it. It might also work with different file formats but I didn't try it either.
Start the Browser and go to your BMP file. Press A to open it and view your BMP file. Press A to open the panel. In the panel you'll find Background. Press A to open it and change your background image.