【PHP】原生验证码

/**
     * author:咔咔
     *
     * 验证码
     */
    public function codeAction() {
        Header("Content-type: image/PNG");
        $rand ="";
        for($i=0;$i<4;$i++){
            $rand.=dechex(rand(0,15));
        }
        $im = imagecreate(100,30);
        $gray = ImageColorAllocate($im, 200,200,200);
        for($i=0;$i<3;$i++){
            $te=imagecolorallocate($im,rand(0,255),rand(0,255),rand(0,255));
        }
        imagefill($im,0,0,$gray);
        while(($rand=rand()%100000)<10000);
        $_SESSION['rand']=$rand;
        imagestring($im, 5, 30, 10, $rand, $te);
        for($i=0;$i<200;$i++)
        {
            $randcolor = ImageColorallocate($im,rand(0,255),rand(0,255),rand(0,255));
            imagesetpixel($im, rand()%100 , rand()%50 , $randcolor);
        }
        imageline($im,0,rand(0,100),100,rand(0,15),$randcolor);
        imageline($im,0,rand(0,100),100,rand(0,15),$randcolor);
        imageline($im,0,rand(0,100),100,rand(0,15),$randcolor);
        ImagePNG($im);
        ImageDestroy($im);
    }