简单好用的PHP验证码类

<?php
/**
* @version 1.0
* @author   bolted snail
* @date 2011-10-15
* @PHP验证码类
* 使用方法：
* $image=new Captcha();
* $image->config('宽度','高度','字符个数','验证码session索引');
* $image->create();//这样就会向浏览器输出一张图片
//http://blog.ddian.cn
* //所有参数都可以省略，
* 默认是：宽80 高20 字符数4 验证码session索引captcha_code
* 第四个参数即把验证码存到$_SESSION['captcha_code']
* 最简单使用示例:
* $image=new Captcha();
* $image->create();//这样就会向浏览器输出一张图片
*/
class Captcha
{
private $width=80,$height=20,$codenum=4;
public $checkcode;     //产生的验证码
private $checkimage;    //验证码图片 
private $disturbColor = ''; //干扰像素
private $session_flag='captcha_code';//存到session中的索引
 
//尝试开始session
function __construct(){
    @session_start();
}
/*
* 参数：（宽度，高度，字符个数）
*/
function config($width='80',$height='20',$codenum='4',$session_flag='captcha_code')
{  
   $this->width=$width;
   $this->height=$height;
   $this->codenum=$codenum;
   $this->session_flag=$session_flag;
}
function create()
{
   //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);
   $_SESSION[$this->session_flag]=$this->checkcode;
}
/*
   * @brief 输出头
   */
private function outFileHeader()
{
   header ("Content-type: image/png");
}
/**
   * 产生验证码
   */
private function createCode()
{
   $this->checkcode = strtoupper(substr(md5(rand()),0,$this->codenum));
}
/**
   * 产生验证码图片
   */
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
}
/**
   * 设置图片的干扰像素 
   */
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);
   }
}
/**
   *
   * 在验证码图片上逐个画上验证码
   *
   */
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+5, $y, $this->checkcode[$i], $bg_color);
   }
}
function __destruct()
{
   unset($this->width,$this->height,$this->codenum,$this->session_flag);
}
}
?>