def METHOD_NAME(self):
    """
    Returns a key for this source that will be used to identify it in
    configuration files, and will be saved in image metadata under Xmp.variety.sourceType.
    Variety will use this source type to find which plugin can handle a particular
    saved image source configuration, so this should not collide between different image
    source plugins.
    :return: source type, e.g. "flickr", "unsplash", etc.
    """
    pass