Returns the path to the custom image set for this game, or None if
        no image is set

def custom_image(self, user):
        """Returns the path to the custom image set for this game, or None if
        no image is set"""
        for ext in self.valid_custom_image_extensions():
            image_location = self._custom_image_path(user, ext)
            if os.path.isfile(image_location):
                return image_location
        return None