Did some checking on the code side vs folder structure
in code img/Background/Background.png vs background.png
in code img/maps/Civilized Realms.png vs
Civilized Realms.PNG
Not sure if the list is complete for there are so many file links in code and it is getting late where I live.
btw I got the Linux fix version from the main mega link in the game download section for the mega link you provided did not work.