いいphp検証コードのクラス

<?php
class Captcha
{
    private $width;
    private $height;
    private $codeNum;
    private $code;
    private $im;

    function __construct($width=80, $height=20, $codeNum=4)
    {
        $this->width = $width;
        $this->height = $height;
        $this->codeNum = $codeNum;
    }

    function showImg()
    {
        //    
        $this->createImg();
        //      
        $this->setDisturb();
        //     
        $this->setCaptcha();
        //    
        $this->outputImg();
    }

    function getCaptcha()
    {
        return $this->code;
    }

    private function createImg()
    {
        $this->im = imagecreatetruecolor($this->width, $this->height);
        $bgColor = imagecolorallocate($this->im, 0, 0, 0);
        imagefill($this->im, 0, 0, $bgColor);
    }

    private function setDisturb()
    { // www.jbxue.com
        $area = ($this->width * $this->height) / 20;
        $disturbNum = ($area > 250) ? 250 : $area;
        //     
        for ($i = 0; $i < $disturbNum; $i++) {
            $color = imagecolorallocate($this->im, rand(0, 255), rand(0, 255), rand(0, 255));
            imagesetpixel($this->im, rand(1, $this->width - 2), rand(1, $this->height - 2), $color);
        }
        //    
        for ($i = 0; $i <= 5; $i++) {
  $color = imagecolorallocate($this->im, rand(128, 255), rand(125, 255), rand(100, 255));
 imagearc($this->im, rand(0, $this->width), rand(0, $this->height), rand(30, 300), rand(20, 200), 50, 30, $color);
        }
    }

    private function createCode()
    {
        $str = "23456789abcdefghijkmnpqrstuvwxyzABCDEFGHIJKMNPQRSTUVWXYZ";
        for ($i = 0; $i < $this->codeNum; $i++) {
            $this->code .= $str{rand(0, strlen($str) - 1)};
        }
    }

    private function setCaptcha()
    {
        $this->createCode();

for ($i = 0; $i < $this->codeNum; $i++) {
    $color = imagecolorallocate($this->im, rand(50, 250), rand(100, 250), rand(128, 250));
            $size = rand(floor($this->height / 5), floor($this->height / 3));
            $x = floor($this->width / $this->codeNum) * $i + 5;
            $y = rand(0, $this->height - 20);
            imagechar($this->im, $size, $x, $y, $this->code{$i}, $color);
        }
    }


    private function outputImg()
    {
        if (imagetypes() & IMG_JPG) {
            header('Content-type:image/jpeg');
            imagejpeg($this->im);
        } elseif (imagetypes() & IMG_GIF) {
            header('Content-type: image/gif');
            imagegif($this->im);
        } elseif (imagetype() & IMG_PNG) {
            header('Content-type: image/png');
            imagepng($this->im);
        } else {
            die("Don't support image type!");
        }
    }
}
?>

<?php
require_once 'captcha.class.php';
$captcha = new Captcha(80,30,4);
$captcha->showImg();
?>