1. put the xxx.png to /SDcard/retroarch/overlay.
2. edit a .cfg file in overlay menu ( step1 ) , change the .png file name in the .cfg file to xxx.png.
3. save the step2 .cfg file as xxx.cfg.
4. in games, quick menu-onscreen overlay, choose the step3 xxx.cfg.
I don't know if I said clearly, my...