验证码在哪加时间的字符串才可以避免读缓存解决方法

randcodelength = 5;
        $this->imgWidth = 80;
        $this->imgHeight = 20;
        $this->codelength = count($this->code)-1;                //获取数组长度当随机范围

        $this->createrandcode();
        $this->createimg();
        $this->createString();
        $this->drawline($this->line);
        $this->ending();

    }
    function createrandcode(){
        for($i=0;$i<$this->randcodelength;$i++){                //初始化验证码
            $this->randcode .= $this->code[rand(0,$this->codelength)];
        }
    }
    function createimg(){                                        //创建图片 前景 背景颜色
        $this->image = imagecreatetruecolor($this->imgWidth,$this->imgHeight);
        $this->background = imagecolorallocate($this->image,0,0,0);
        $this->foreground = imagecolorallocate($this->image,255,255,255);
    }
    function createString(){                                    //创建字符串
        imagestring($this->image,5,rand(5,35),0,$this->randcode,$this->foreground);
    }
    function drawline($some){
        for($i=0;$i<$some;$i++){
            imageline($this->image,rand(1,$this->imgWidth),rand(1,$this->imgHeight),rand(1,$this->imgWidth),rand(1,$this->imgHeight),$this->foreground);
        }
    }
    function ending(){
        ob_clean();                                    //抛弃缓存内容
        header("Content-type: image/jpeg");
        imagejpeg($this->image);
    }
}
?>