updated
https://github.com/finalburnneo/FBNeo-extras with the latest additions/modifications
@7zxkv i think the repo has some thumbnails that might be missing from the packs
additional note:
i have also been wondering what's the aspect ratio we should use for thumbnails, a lot of those thumbnails are using the 1:1 pixel aspect ratio (meaning a width:height display aspect ratio), but it seems to me that it'd make more sense if our thumbnails respected the game's intended display aspect ratio (4:3, 3:4, etc...). Some thumbnails, especially from vertical games, look kind of weird if you don't, there are even some cases where a vertical game has higher width than height if you ignore the display aspect ratio (ex.:
mustache).