PHP的中问验证码

<?php
class code
{
 var $width =160; //图片的宽
 var $hight =40; //图片的高
 var $image;
 var $red =223; //图片的rgb颜色
 var $green =225; //红
 var $blue =227 ;//绿
 var $pix =227 ;//蓝
 var $pixcolor; //杂色颜色;
 var $pixred = 242; //红
 var $pixgreen = 168;//绿
 var $pixblue = 162; //蓝
 var $txt=null;//验证码文字
 var $txtcode=null;
 var $txtsub=null;
 var $pixnum = 300; //杂点数量
 var $i=0;
 var $widthpx=0;
 var $highty=0;
 var $txtreg=50;
 var $txtgreen=30;
 function createimage()  //创建一张图并填色
 {
  $this->image = imagecreate($this->width,$this->hight);
  $this->color = imagecolorallocate($this->image,$this->red,$this->green,$this->blue);
  return imagefill($this->image,0,0,$this->color);
 }
 function createpix() //干扰因素
 {
  for($this->i=1;$this->i<$this->pixnum;$this->i++)
  {
    $this->widthpx = rand(0,$this->width);
    $this->highty = rand(0,$this->hight);
   $this->pixcolor = imagecolorallocate($this->image,$this->pixred,$this->pixgreen,$this->pixblue);
     imagesetpixel($this->image,$this->widthpx,$this->highty,$this->pixcolor);
  }
 }
  function gettxt() //创建验证码文字
 {
  $this->txt = array("我","爱","你","叶","就","慧","明","发","真","的","很","想","不","知","到","为","什","么","就","是","忘","不","了","你","也","许","上","辈","欠","钱");
  for($this->i=0;$this->i<6;$this->i++)
  {
   $this->sub = $this->txt[rand(0,29)];
   $this->txtcode.= $this->sub;
  }
  $this->txtcode = iconv("gb2312","utf-8",$this->txtcode);
  $_session["code"] = $this->txtcode; //产生的验证id
 }
 function createstring() //创建验证码图片
 {
  imagettftext($this->image,20,5,0,40,$this->pixcolor,"c:\windows\fonts\simsun.ttc ",$this->txtcode);
  header("content-type:image/png");
  return imagepng($this->image);
     imagedestroy($this->image);
 }
 function getcodeimage()//获得验证码图片
 {
  $this->createimage();
  $this->gettxt();
  $this->createpix();  
  $this->createstring();
 }
}
?>
<?php 
session_start();   
$text = new code;
$text->createimage();
$text->gettxt();
$text->createpix();
$text->createstring();
?>