Ok, so i discovered Acies painting kit.
I replaced the gray area in the .psd with a my picture gimp.
Then i exported it as .psd in custom_stories/[My Customstory]/static_objects/paintings/custom_painting01/
(Replacing the customPainting_Base.psd)
I can open the file in the editor, but the gray area that i replaced is still gray
I tried opening the .psd file in gimp, directly from it's path (mentioned above), and the gray area IS replaced with the right picture. it just doesn't show up in either the game or the editor.
What did i do wrong here?
Gimp
Editor
Trying is the first step to success.