Hello again!
I'm using 1.2.3, and i followed the steps that led to the creation of mods/installs, indeed. (Yuti's 1.2.1 only, no other mods added)
What i see in www/img/characters is that i can guess that every image from the base game has .png extensions, except the images from the mod, which has the .rpgmvp extension.
Example: $DIDOverlaySeles.png, and $DIDOverlaySelesBandit.rpgmvp