@alepinay the idea of adding an actual screenshot to each save file is indeed under consideration using this library, however some stuff has kept us from actually implement it.
The images saved must be clean screenshots of the game in that moment without any additional styling (i.e. cartdrige appearance) since that should be implemented per game by styling the save slots. That way, every game can do whatever fits best for it.
Because we can't save the image externally (save files are not actual files), we'd also need to make the move to IndexedDB instead of LocalStorage for save files as LocalStorage can not store that much data (Images are heavy!). For that very reason, before taking the decision of moving to IndexedDB we need to do some stress testing to see if the storage doesn't get slow or has any problems when too many images are saved inside of it, saving images in a database is generally a bad idea and would likely come with a limit in how many save files we can allow.
Changing storages in v2 is pretty simple but if performance is not great then we'll have to stick with the current slot images/backgrounds.