PHP verification code class example sharing

<?php
header(&#39;Content-type:text/html;charset=utf8&#39;);
class Code{
  // 验证码个数$number
  protected $number;
  // 验证码类型$codeType
  protected $codeType;
  // 验证码图像宽度$width
  protected $width;
  // 验证码$height
  protected $height;
  // 验证码字符串$code
  protected $code;
  // 图像资源$image
  protected $image;
  
  public function __construct($number=4,$codeType=0,$height=50,$width=100){
    //初始化自己的成员属性
    $this->number=$number;
    $this->codeType=$codeType;
    $this->width = $width;
    $this->height= $height;
    
    //生成验证码函数
    $this->code = $this ->createCode();
    
  }
  public function __get($name){
    if ($name == &#39;code&#39;){
      return $this->code;
    }
    return false;
  }
  /*获取验证码*/
  public function getCode() {
    return $this->code;
  }
  /*图像资源销毁*/
  public function __destruct(){
    imagedestroy($this->image);
  }
  protected function createCode(){
    //通过你的验证码类型生成验证码
    switch ($this->codeType){
      case 0: //纯数字
        $code = $this->getNumberCode();
        break;
      case 1: //纯字母的
        $code = $this->getCharCode();
        break;
      case 2: //数字和字母混合
        $code = $this->getNumCharCode();
        break;
      default:
        die(&#39;不支持此类验证码类型&#39;);
    }
    return $code;
  }
  protected function getNumberCode(){
    $str = join(&#39;&#39;, range(0, 9));
    return substr(str_shuffle($str),0, $this->number);
  }
  protected function getCharCode(){
    $str = join(&#39;&#39;, range(&#39;a&#39;, &#39;z&#39;));
    $str = $str.strtoupper($str);
    return substr(str_shuffle($str),0,$this->number);
  }
  protected function getNumCharCode(){
    $numstr = join(&#39;&#39;,range(0, 9));
    $str =join(&#39;&#39;, range(&#39;a&#39;, &#39;z&#39;));
    $str =$numstr.$str.strtoupper($str);
    return substr(str_shuffle($str), 0,$this->number);
  }
  protected function createImage(){
    $this->image = imagecreatetruecolor($this->width, 
        $this->height);
  }
  protected function fillBack(){
    imagefill($this->image, 0, 0, $this->lightColor());
  }
  /*浅色*/
  protected function lightColor(){
    return imagecolorallocate($this->image, mt_rand(133,255), mt_rand(133,255), mt_rand(133,255));
  }
  /*深色*/
  protected function darkColor(){
    return imagecolorallocate($this->image, mt_rand(0,120), mt_rand(0,120), mt_rand(0,120));
  }
  protected function drawChar(){
    $width = ceil($this->width / $this->number);
    for ($i=0; $i< $this->number;$i++){
      $x = mt_rand($i*$width+5, ($i+1)*$width-10);
      $y = mt_rand(0, $this->height -15);
      imagechar($this->image, 5, $x, $y, $this->code[$i], $this->darkColor());
    }
  }
  protected function drawLine(){
    for ($i=0;$i<5;$i++) {
      imageline($this->image,mt_rand(0,$this->width),mt_rand(0,$this->height),mt_rand(0,$this->width),mt_rand(0,$this->height),$this->darkColor());
    }
  }
  protected function drawDisturb(){
    for ($i=0;$i<150;$i++){
      $x=mt_rand(0, $this->width);
      $y=mt_rand(0, $this->height);
      imagesetpixel($this->image, $x, $y, $this->lightColor());
    }
  }
  protected function show(){
    header(&#39;Content-Type:image/png&#39;);
    imagepng($this->image);
  }
  public function outImage(){
//     创建画布
    $this->createImage();
//     填充背景色
    $this->fillBack();
//     将验证码字符串花到画布上
    $this->drawChar();
//     添加干扰元素
    $this->drawDisturb();
//     添加线条
    $this->drawLine();
//     输出并显示
    $this->show();
  }
}

<?php
//开启session
session_start();
require_once &#39;code.php&#39;;

$code= new Code(4,1,50,100);
$_SESSION[&#39;code&#39;]= $code->getCode();
$code->outImage();

<?php 
    //开启Session 
    session_start(); 
    //判断是否提交 
    if(isset($_POST[&#39;dosubmit&#39;])){ 
      //获取session中的验证码并转为小写 
      $sessionCode=strtolower($_SESSION[&#39;code&#39;]); 
      //获取输入的验证码 
      $code=strtolower($_POST[&#39;code&#39;]); 
      //判断是否相等 
      if($sessionCode==$code){ 
        echo "<script type=&#39;text/javascript&#39;>alert(&#39;验证码正确!&#39;);</script>"; 
      }else{ 
        echo "<script type=&#39;text/javascript&#39;>alert(&#39;验证码错误!&#39;);</script>"; 
      } 
    } 
  ?> 
  <!DOCTYPE html> 
  <html> 
    <head> 
      <title></title> 
      <meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/> 
      <style type="text/css"> 
        *{margin:0px;padding:0px;} 
        ul{ 
          width:400px; 
          list-style:none; 
          margin:50px auto; 
        } 
         
        li{ 
          padding:12px; 
          position:relative; 
        } 
         
        label{ 
          width:80px; 
          display:inline-block; 
          float:left; 
          line-height:30px; 
        } 
         
        input[type=&#39;text&#39;],input[type=&#39;password&#39;]{ 
          height:30px; 
        } 
         
        img{ 
          margin-left:10px; 
        } 
         
        input[type="submit"]{ 
          margin-left:80px; 
          padding:5px 10px; 
        } 
      </style> 
    </head> 
    <body> 
      <form action="login.php" method="post"> 
        <ul> 
          <li> 
            <label>用户名：</label> 
            <input type="text" name="username"/> 
          </li> 
          <li> 
            <label>密码：</label> 
            <input type="password" name="password"/> 
          </li> 
          <li> 
            <label>验证码：</label> 
            <input type="text" name="code" size="4" style="float:left"/> 
            <img src="test.php" onclick="this.src=&#39;test.php?Math.random()&#39;"/> 
          </li> 
          <li> 
            <input type="submit" value="登录" name="dosubmit"/> 
          </li> 
        </ul> 
      </form> 
    </body> 
  </html>