Hello exactly as 0readingcomprehension said.You need to add a picture of your designated logo to the 'upload' folder.
It has to be 16x12 pixels wide and it works for certain formats only.
I've used .bmp successfully.
You will find a tutorial on the 'Guilds' wiki page, well, not WoM's because that's not a thing :/
I can't link it due to obvious reasons, but a quick google search with the query 'metin2 wiki guilds' should be enough.
You can use free online tools to resize, change file format and keep transparency.
Good luck!
Paint.net lets you create a canvas in any sizeThis is a plus not related to the game*: Someone know an editor to create 16x12 pixel images from scratch ?
This is not needed anymore. Just use the .tga format and remove all pixels that you want to be transparent.If you want transparency, fill the area that you want to be transparent with color pink
#FF00FF