PHP生成Gif图片验证码(3)

private static function AddHeader() {
        $i = 0;
        if (ord(self::$BUF[0]{10}) & 0x80) {
            $i = 3 * (2 << (ord(self::$BUF[0]{10}) & 0x07));
            self::$Img .= substr(self::$BUF[0], 6, 7);
            self::$Img .= substr(self::$BUF[0], 13, $i);
            self::$Img .= "!\377\13NETSCAPE2.0\3\1" . chr(self::$LOP & 0xFF) . chr((self::$LOP >> 8) & 0xFF) . "\0";
        }
        unset($i);
    }