def METHOD_NAME(youtube_id):
    """
    Download highest resoultion video thumbnail available from youtube.
    """
    thumbnail_content = thumbnail_content_type = None
    # Download highest resolution thumbnail available.
    for thumbnail_quality in YOUTUBE_THUMBNAIL_SIZES:
        thumbnail_url = urljoin('https://img.youtube.com', '/vi/{youtube_id}/{thumbnail_quality}.jpg'.format(
            youtube_id=youtube_id, thumbnail_quality=thumbnail_quality
        ))
        response = requests.get(thumbnail_url)
        if response.status_code == requests.codes.ok:   # pylint: disable=no-member
            thumbnail_content = response.content
            thumbnail_content_type = response.headers['content-type']
            # If best available resolution is found, don't look for lower resolutions.
            break
    return thumbnail_content, thumbnail_content_type