验证码

gd库画图流程：

1，创建画布

2，创建各种颜料

3，绘画

4，保存成图片

5，销毁

html页面

<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>验证</title>
<script type="text/javascript">
function update(th){
    th.src='001.php?_s='+Math.random();
}
</script>
</head>
<body>
    <form action='' method=''>
        验证码<input type='text' name='验证码'/><img src='001.php' onclick='update(this)'/><br/>
        <input type='submit' value='提交'/>
    </form>
</body>
</html>

001.php生成验证码

<?php
// print_r(gd_info());//判断gd2库是否开启

$rs=imagecreatetruecolor(50,30);//创建画布资源
$gray=imagecolorallocate($rs, 100, 100, 100);

$fontcolor=imagecolorallocate($rs, mt_rand(150,255), mt_rand(150,255), mt_rand(150,255));

$linecolor1=imagecolorallocate($rs, mt_rand(100,200), mt_rand(100,200), mt_rand(100,200));
$linecolor2=imagecolorallocate($rs, mt_rand(100,200), mt_rand(100,200), mt_rand(100,200));
$linecolor3=imagecolorallocate($rs, mt_rand(100,200), mt_rand(100,200), mt_rand(100,200));

//填充颜色
imagefill($rs, 0, 0, $gray);

//随机字符串
$str=substr(str_shuffle('ABCDEFGHJKMNOPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz23456789'),0,4);

//书写字符串
imagestring($rs, 5, 8, 5, $str, $fontcolor);

//画干扰线
imageline($rs,0,mt_rand(0,30),50,mt_rand(0,30),$linecolor1);
imageline($rs,0,mt_rand(0,30),50,mt_rand(0,30),$linecolor2);
imageline($rs,0,mt_rand(0,30),50,mt_rand(0,30),$linecolor3);

//输出
header('content-type:image/png');
imagepng($rs);
//销毁
imagedestroy($rs);
?>