Simply add your images into the Images folder (Ideally ones that are 640x512 although my app can resize them but they may look off afterwards depending on the original size) and launch the app then click your image and then click Convert Image and optionally change the font color, Then select which theme preset to apply it too, After you receive the popup saying it's done, Go into the Images folder and you'll find your theme/themes named cust_0 to cust_9.
Inside the folders you should only find the following and nothing else:
- bg_l.pvr
- bg_r.pvr
- theme.ini
Once you have converted your theme/themes you'll need to place them in the GDMENU Card Manager/tools/openMenu/menu_data/theme/ folder then rebuild OpenMenu on your sd card in GDMENU Card Manager.
I've also included a simple template to help you get started.