php5 verification code class (simple and practical)

<?php
/**
* php5验证码类
* edit bbs.it-home.org
*/
class CCheckCodeFile
{
//验证码位数
private $mCheckCodeNum   = 4;

//产生的验证码
private $mCheckCode    = '';

//验证码的图片
private $mCheckImage   = '';

//干扰像素
private $mDisturbColor   = '';

//验证码的图片宽度
private $mCheckImageWidth = '80';

//验证码的图片宽度
private $mCheckImageHeight   = '20';

/**
*
* @brief   输出头
*
*/
private function OutFileHeader()
{
   header ("Content-type: image/png");
}

/**
*
* @brief   产生验证码
*
*/
private function CreateCheckCode()
{
   $this->mCheckCode = strtoupper(substr(md5(rand()),0,$this->mCheckCodeNum));
   return $this->mCheckCode;
}

/**
*
* @brief   产生验证码图片
*
*/
private function CreateImage()
{
   $this->mCheckImage = @imagecreate ($this->mCheckImageWidth,$this->mCheckImageHeight);
   imagecolorallocate ($this->mCheckImage, 200, 200, 200);
   return $this->mCheckImage;
}

/**
*
* @brief   设置图片的干扰像素
*
*/
private function SetDisturbColor()
{
   for ($i=0;$i<=128;$i++)
   {
    $this->mDisturbColor = imagecolorallocate ($this->mCheckImage, rand(0,255), rand(0,255), rand(0,255));
    imagesetpixel($this->mCheckImage,rand(2,128),rand(2,38),$this->mDisturbColor);
   }
}

/**
*
* @brief   设置验证码图片的大小
*
* @param   $width   宽
*
* @param   $height 高 
*
*/
public function SetCheckImageWH($width,$height)
{
   if($width==''||$height=='')return false;
   $this->mCheckImageWidth   = $width;
   $this->mCheckImageHeight = $height;
   return true;
}

/**
*
* @brief   在验证码图片上逐个画上验证码
*
*/
private function WriteCheckCodeToImage()
{
   for ($i=0;$i<=$this->mCheckCodeNum;$i++)
   {
    $bg_color = imagecolorallocate ($this->mCheckImage, rand(0,255), rand(0,128), rand(0,255));
    $x = floor($this->mCheckImageWidth/$this->mCheckCodeNum)*$i;
    $y = rand(0,$this->mCheckImageHeight-15);
    imagechar ($this->mCheckImage, 5, $x, $y, $this->mCheckCode[$i], $bg_color);
   }
}

/**
*
* @brief   输出验证码图片
*
*/
public function OutCheckImage()
{
   $this ->OutFileHeader();
   $this ->CreateCheckCode();
   $this ->CreateImage();
   $this ->SetDisturbColor();
   $this ->WriteCheckCodeToImage();
   imagepng($this->mCheckImage);
   imagedestroy($this->mCheckImage);
}
}
$c_check_code_image = new CCheckCodeFile();
//$c_check_code_image ->SetCheckImageWH(100,50);//设置显示验证码图片的尺寸
$c_check_code_image ->OutCheckImage();
?>