php图像验证码生成代码

<?php 
  class TestCode{//创建类名为TestCode 
   private $width; 
   private $height; 
   private $str; 
   private $im; 
   private $strColor;    
   function __construct($width,$height){ 
    $this->width=$width; 
    $this->height=$height; 
    $this->str=$_GET['code']; 
    $this->createImage(); 
   } 
   function createImage(){ 
    $this->im=imagecreate($this->width,$this->height);//创建画布 
    imagecolorallocate($this->im,200,200,200);//为画布添加颜色 
    for($i=0;$i<4;$i++){//循环输出四个数字 
     $this->strColor=imagecolorallocate($this->im,rand(0,100),rand(0,100),rand(0,100)); 
     imagestring($this->im,rand(3,5),$this->width/4*$i+rand(5,10),rand(2,5),$this->str[$i],$this->strColor); 
    } 
    for($i=0;$i<200;$i++){//循环输出200个像素点 
     $this->strColor=imagecolorallocate($this->im,rand(0,255),rand(0,255),rand(0,255)); 
     imagesetpixel($this->im,rand(0,$this->width),rand(0,$this->height),$this->strColor); 
    } 
   } 
   function show(){// 
    header('content-type:image/png');//定义输出为图像类型 
    imagepng($this->im);//生成图像 
    imagedestroy($this->im);//销毁图像释放内存 
   } 
  } 
  $image=new TestCode(80,20);//将类实例化为对象 
  $image->show();//调用函数 
?>