def resize_thumbnails(pelican):
    """ Resize a directory tree full of images into thumbnails

    :param pelican: The pelican instance
    :return: None
    """
    global enabled
    if not enabled:
        return

    in_path = _image_path(pelican)

    include_regex = pelican.settings.get('THUMBNAIL_INCLUDE_REGEX')
    if include_regex:
        pattern = re.compile(include_regex)
        is_included = lambda name: pattern.match(name)
    else:
        is_included = lambda name: not name.startswith('.')

    sizes = pelican.settings.get('THUMBNAIL_SIZES', DEFAULT_THUMBNAIL_SIZES)
    resizers = dict((k, _resizer(k, v, in_path)) for k,v in sizes.items())
    logger.debug("Thumbnailer Started")
    for dirpath, _, filenames in os.walk(in_path):
        for filename in filenames:
            if is_included(filename):
                for name, resizer in resizers.items():
                    in_filename = path.join(dirpath, filename)
                    out_path = get_out_path(pelican, in_path, in_filename, name)
                    resizer.resize_file_to(
                        in_filename,
                        out_path, pelican.settings.get('THUMBNAIL_KEEP_NAME'))
Resize a directory tree full of images into thumbnails

    :param pelican: The pelican instance
    :return: None