def detect_file(filename):
    """Decide what to do with the file."""
    image_format = get_image_format(filename)

    if image_format in Settings.formats:
        return image_format

    if image_format in (NONE_FORMAT, ERROR_FORMAT):
        return None

    if Settings.verbose > 1 and not Settings.list_only:
        print(filename, image_format, 'is not a enabled image or '
              'comic archive type.')
    return None