public static function isAnimatedGif($fileName)
    {
        if (($fh = fopen($fileName, 'rb')) === false) {
            throw new \RuntimeException('Can\'t open ' . $fileName, 1454678600);
        }
        $count = 0;
        // An animated gif contains multiple "frames", with each frame having a
        // header made up of:
        // - a static 4-byte sequence (\x00\x21\xF9\x04)
        // - 4 variable bytes
        // - a static 2-byte sequence (\x00\x2C)

        // We read through the file til we reach the end of the file, or we've found
        // at least 2 frame headers
        while (!feof($fh) && $count < 2) {
            $chunk = fread($fh, 1024 * 100); // read 100kb at a time
            $count += preg_match_all('#\x00\x21\xF9\x04.{4}\x00[\x2C\x21]#s', $chunk, $matches);
        }

        fclose($fh);
        return $count > 1;
    }