PHP verification code file class

class CCheckCodeFile
{
//Number of verification code digits
private $mCheckCodeNum = 4;

//Generated verification code
private $mCheckCode = '';

//Verification code Picture
private $mCheckImage = '';

//Interference pixel
private $mDisturbColor = '';

//Verification code picture width
private $mCheckImageWidth = '80';

//Verification code picture Width
private $mCheckImageHeight = '20';

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

/**
*
* @brief generates verification code
*
*/
private function CreateCheckCode()
{
 $this->mCheckCode = strtoupper(substr(md5(rand()),0,$this->mCheckCodeNum));
 return $this->mCheckCode ;
}

/**
*
* @brief generates verification code image
*
*/
private function CreateImage()
{
 $this->mCheckImage = @imagecreate ($this->mCheckImageWidth,$this->mCheckImageHeight);
 imagecolorallocate ( $this->mCheckImage, 200, 200, 200);
 return $this->mCheckImage;
}

/**
*
* @brief Set the interference pixels of the image
*
*/
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 Set the size of the verification code image
*
* @param $width width
*
* @param $height height
*
*/
public function SetCheckImageWH($width,$height)
{
 if($width==''||$height=='')return false;
 $this->mCheckImageWidth = $width;
 $this->mCheckImageHeight = $height;
 return true;
 }

/**
*
* @brief Draw the verification codes one by one on the verification code picture
*
*/
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 Output verification code picture
*
*/
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);//Set the size of the verification code image
$c_check_code_image ->OutCheckImage();
?>

Verification code, PHP