if you are loading from Main.py
you need to do it like this:
bkg = pygame.image.load("Package/Resources/BKg.png").convert_alpha()
or
bkg = pygame.image.load(os.path.join("Package","Resources","BKg.png")).convert_alpha()
because yopure structure says Resources
is in Package
just because you imported from the Package
directory doesn't mean you can load images from it