Here you can browse for a BMP file to import as a background.

Your import files should be saved in BMP format with a bit depth of 8-bit (256 colors) or 24-bit (millions of colors)

The correct size for a background is 320x200 pixels. The pixel size must be exactly correct.

The browser will display the size and bit depth of any BMP file you select, so you can easily identify files that will fail to import because they have the wrong pixel size or the wrong bit depth.