Godot Version
4.3
You can use FileDialog to let user upload there own image file and put in your game.
yes and no.
there are two problems to solve here, one is allowing the player to use an image or some generated resource in godot. I’m not sure this is possible since these would have to be in a pck file.
if it’s with a pck, players could create a scene in godot (the editor) and use it like a mod, but they could use this to spread malicious code if it is shared without controls.
maybe it is possible to load an image from a different path.
once you have the image this can be used in the game.
the second problem is not a godot problem but web.
you need a server to upload the skins to and to store them, and from where players can download the skins. this is not my area of expertise, you need code in godot to connect to the server and you need to setup the server to receive and send the data/skins.