Some issues with thumbnails

Hello there !

I’m using the Ps Vita version of Retroarch. I’m running into thumbnails problem. Some of them don’t appear in the playlist such as Gameboy Color, for exemple.

I guess I miss around something… So can someone explain me the necessary conditions to make a group of thumbnails appear for a game ?

Another question : what if a want to add a brend new game with personnal thumbnails (for a romhack for exemple) ? Do I have to manually edit the database ? If so, how ?

Thanks in advance,

Vilikt