BabasChess requires the background images be a bitmap. You cannot load .png, or .jpeg .jpg or any other image type. It must be .bmp
This doesn't present a big problem as long as you have the right image editing tools.
1) Google the image you want and save it. For me, it was 'dark wood'
2) Convert the image to bitmap (skip this step if your image is already in bitmap type)
2a) Open your image edit tool. For me, I use SnagIt. But any basic edit tool should work.
2b) Convert the image type. Depending on the tool you are using, this step may vary. But if you are using SnagIt, there is a 'Convert Image' option. Using the wizard, it walks you through ... at the right step, choose the .bmp option. Windows Paint program can also convert images to bitmaps. Open the image, and then simply choose, 'save as' and choose bitmap.
3) Save the bitmap (or copy it) to the Data/Backgrounds directory in the folder where BabasChess is stored. For me it is C:\Program Files\BabasChess\BabasChess\Data\Backgrounds
4) Open Preferences (F11) in BabasChess and choose the background.