注册和登录时的验证码

<?php

class Captcha_code
{
var $width='60';
var $num='4';
var $height='20';
var $name='randcode';

function show()
{
Header("Content-type: image/gif");
/*
* 初始化
*/
$border = 0; //是否要边框 1要:0不要
$how = $this->num; //验证码位数
$w = $this->width; //图片宽度
$h = $this->height; //图片高度
$fontsize = 5; //字体大小
$alpha = "abcdefghijkmnopqrstuvwxyz"; //验证码内容1:字母
$number = "023456789"; //验证码内容2:数字
$randcode = ""; //验证码字符串初始化
srand((double)microtime()*1000000); //初始化随机数种子

$im = ImageCreate($w, $h); //创建验证图片

/*
* 绘制基本框架
*/
$bgcolor = ImageColorAllocate($im, 255, 255, 255); //设置背景颜色
ImageFill($im, 0, 0, $bgcolor); //填充背景色
if($border)
{
$black = ImageColorAllocate($im, 0, 0, 0); //设置边框颜色
ImageRectangle($im, 0, 0, $w-1, $h-1, $black);//绘制边框
}

/*
* 逐位产生随机字符
*/
for($i=0; $i<$how; $i++)
{
$alpha_or_number = mt_rand(0, 1); //字母还是数字
$str = $alpha_or_number ? $alpha : $number;
$which = mt_rand(0, strlen($str)-1); //取哪个字符
$code = substr($str, $which, 1); //取字符
$j = !$i ? 4 : $j+15; //绘字符位置
$color3 = ImageColorAllocate($im, mt_rand(0,100), mt_rand(0,100), mt_rand(0,100)); //字符随即颜色
ImageChar($im, $fontsize, $j, 3, $code, $color3); //绘字符
$randcode .= $code; //逐位加入验证码字符串
}

/*
* 添加干扰
*/
for($i=0; $i<5; $i++)//绘背景干扰线
{
$color1 = ImageColorAllocate($im, mt_rand(0,255), mt_rand(0,255), mt_rand(0,255)); //干扰线颜色
ImageArc($im, mt_rand(-5,$w), mt_rand(-5,$h), mt_rand(20,300), mt_rand(20,200), 55, 44, $color1); //干扰线
}
for($i=0; $i<$how*15; $i++)//绘背景干扰点
{
$color2 = ImageColorAllocate($im, mt_rand(0,255), mt_rand(0,255), mt_rand(0,255)); //干扰点颜色
ImageSetPixel($im, mt_rand(0,$w), mt_rand(0,$h), $color2); //干扰点
}

//把验证码字符串写入session
$CI = &get_instance();

$CI->load->library('session');

$randcode = md5($randcode);

$CI->session->set_userdata('code',$randcode);

/*绘图结束*/
Imagegif($im);
ImageDestroy($im);
/*绘图结束*/
}
}
?>

验证码：<input id="verify_text" name="verify_text" type="text">
<img src="http://gameapi.xiaoyou-game.com/user/verify_image"   id="verify_code">
看不清？<a href="javascript:changeCode();">换一张</a>

<script type="text/javascript">
function changeCode(){
$("#verify_code").attr("src","http://gameapi.xiaoyou-game.com/user/verify_image?r="+Math.random());
}
</script>

public function verify_image()
{
$this->load->library('captcha_code');
ob_clean();
$this->captcha_code->show();
}

$verify_text = md5($post['verify_text']);
$verify_code = $this->session->userdata('code');
//两相比较即可，若相同，则验证码成功