PHP complex generation of verification code images_PHP tutorial

function image3($length=4,$type='png',$width=180,$height=60,$fontface='fpnf.ttf',$verifyName='verify') {
        $code = $this->rand_string($length,4);
        $width = ($length*25)>$width?$length*25:$width;
        $authCode = new Zend_Session_Namespace('Auth_Code');
        $authCode->imagecode = $randval;
       
        $im=imagecreatetruecolor($width,$height);
        $borderColor = imagecolorallocate($im, 100, 100, 100);                    //边框色
        $bkcolor=imagecolorallocate($im,250,250,250);
        imagefill($im,0,0,$bkcolor);
        @imagerectangle($im, 0, 0, $width-1, $height-1, $borderColor);
        // 干扰
        for($i=0;$i<15;$i++){
            $fontcolor=imagecolorallocate($im,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
            imagearc($im,mt_rand(-10,$width),mt_rand(-10,$height),mt_rand(30,300),mt_rand(20,200),55,44,$fontcolor);
        }
        for($i=0;$i<255;$i++){
            $fontcolor=imagecolorallocate($im,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
            imagesetpixel($im,mt_rand(0,$width),mt_rand(0,$height),$fontcolor);
        }
        if(!is_file($fontface)) {
            $fontface = dirname(__FILE__)."/".$fontface;
        }
        for($i=0;$i<$length;$i++){
            $fontcolor=imagecolorallocate($im,mt_rand(0,120),mt_rand(0,120),mt_rand(0,120)); //这样保证随机出来的颜色较深。
            $codex= substr($code,$i,1);
            imagettftext($im,mt_rand(16,20),mt_rand(-60,60),40*$i+20,mt_rand(30,35),$fontcolor,$fontface,$codex);
        }
        $this->output($im,$type);
    }
   
    function output($im,$type='png')
    {
        header("Content-type: image/".$type);
        $ImageFun='Image'.$type;
        $ImageFun($im);
        imagedestroy($im);
    }