php验证码

<?php

session_start();

function random($len) {
$srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm";
mt_srand();
$strs = "";
for ($i = 0; $i < $len; $i++) {
$strs .= $srcstr[mt_rand(0, 30)];
}
return $strs;
}

//随机生成的字符串
$str = random(4);

//验证码图片的宽度
$width  = 50;

//验证码图片的高度
$height = 25;

//声明需要创建的图层的图片格式
@ header("Content-Type:image/png");

//创建一个图层
$im = imagecreate($width, $height);

//背景色
$back = imagecolorallocate($im, 0xFF, 0xFF, 0xFF);

//模糊点颜色
$pix  = imagecolorallocate($im, 187, 230, 247);

//字体色
$font = imagecolorallocate($im, 41, 163, 238);

//绘模糊作用的点
mt_srand();
for ($i = 0; $i < 1000; $i++) {
imagesetpixel($im, mt_rand(0, $width), mt_rand(0, $height), $pix);
}

//输出字符
imagestring($im, 5, 7, 5, $str, $font);

//输出矩形
imagerectangle($im, 0, 0, $width -1, $height -1, $font);

//输出图片
imagepng($im);

imagedestroy($im);

$str = md5($str);

//选择 cookie
//SetCookie("verification", $str, time() + 7200, "/");

//选择 Session

$_SESSION["verification"]= $str;

?>

<script type="text/javascript">
<!--验证码刷新-->
function changing(){
document.getElementById('checkpic').src="../../class/checkcode.php?"+Math.random();
}
</script>

<div>请输入验证码<img id="checkpic" onclick="changing();"  src="../../class/checkcode.php" />点击刷新</div>