<?php 
 
class ValidationCode 
{ 
private $width,$height,$codenum; 
public $checkcode;   //产生的验证码 
private $checkimage;  //验证码图片 
private $disturbColor = ''; //干扰像素 
 
function __construct($width='80',$height='20',$codenum='4') 
{ 
  $this->width=$width; 
  $this->height=$height; 
  $this->codenum=$codenum; 
} 
function outImg() 
{ 
  //输出头 
  $this->outFileHeader(); 
  //产生验证码 
  $this->createCode(); 
 
  //产生图片 
  $this->createImage(); 
  //设置干扰像素 
  $this->setDisturbColor(); 
  //往图片上写验证码 
  $this->writeCheckCodeToImage(); 
  imagepng($this->checkimage); 
  imagedestroy($this->checkimage); 
} 
 
private function outFileHeader() 
{ 
  header ("Content-type: image/png"); 
} 
 
private function createCode() 
{ 
  $this->checkcode = strtoupper(substr(md5(rand()),0,$this->codenum)); 
} 
 
private function createImage() 
{ 
  $this->checkimage = @imagecreate($this->width,$this->height); 
  $back = imagecolorallocate($this->checkimage,255,255,255); 
  $border = imagecolorallocate($this->checkimage,0,0,0);  
  imagefilledrectangle($this->checkimage,0,0,$this->width - 1,$this->height - 1,$back); // 白色底 
  imagerectangle($this->checkimage,0,0,$this->width - 1,$this->height - 1,$border);  // 黑色边框 
} 
 
private function setDisturbColor() 
{ 
  for ($i=0;$i<=200;$i++) 
  { 
  $this->disturbColor = imagecolorallocate($this->checkimage, rand(0,255), rand(0,255), rand(0,255)); 
  imagesetpixel($this->checkimage,rand(2,128),rand(2,38),$this->disturbColor); 
  } 
} 
 
private function writeCheckCodeToImage() 
{ 
  for ($i=0;$i<=$this->codenum;$i++) 
  { 
  $bg_color = imagecolorallocate ($this->checkimage, rand(0,255), rand(0,128), rand(0,255)); 
  $x = floor($this->width/$this->codenum)*$i; 
  $y = rand(0,$this->height-15); 
  imagechar ($this->checkimage, rand(5,8), $x, $y, $this->checkcode[$i], $bg_color); 
  } 
} 
function __destruct() 
{ 
  unset($this->width,$this->height,$this->codenum); 
} 
} 
?> 

<?php 
session_start(); 
require_once('CreateImg.class.php'); 
$image = new ValidationCode('80','20','4');  //图片长度、宽度、字符个数 
$image->outImg(); 
$_SESSION['validationcode'] = $image->checkcode; //存贮验证码到 $_SESSION 中 
?>

?php 
session_start(); 
$test = $_POST['test']; 
$test = strtoupper(trim($test)); 
$submit = $_POST['submit']; 
if(isset($submit)){ 
if($test==$_SESSION['validationcode']){ 
  echo 'true'; 
} else { 
  echo 'false'; 
} 
} 
?>