一个不错的php验证码的类

类的代码：

 <?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()
     {
         //创建图片
         $this->createImg();
         //设置干扰元素
         $this->setDisturb();
         //设置验证码
         $this->setCaptcha();
         //输出图片
         $this->outputImg();
     }
 //http://www.cnblogs.com/sosoft/
     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()
     {
         $area = ($this->width * $this->height) / 20;
         $disturbNum = ($area > 250) ? 250 : $area;
         //加入点干扰
         for ($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), $color);
         }
         //加入弧线
         for ($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!");
         }
     }

 }
?>

使用的一个例子：

<?php
require_once 'captcha.class.php';

$captcha = new Captcha(80,30,4);

$captcha->showImg();

?>