PHP验证码代码

为OJ写的一个验证码代码。

<?php
/****************************************
*  验证码 v0.9
*  Powerd by awaysoft.com
*  本组件采用GPLv3发布
*  2011-07-15
****************************************/
/* $len 为随机字符串长度，$type为类型，a为字符数字，c为字符,n为数字， 已经去除可能误导的字符 */
function get_rand_string($len=4, $type="n"){
if ($len < 0) $len = 4;
if ($type == 'a') $chars = 'ABCDEFGHJKMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz023456789';
else if ($type == 'c') $chars = 'ABCDEFGHJKMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz';
else if ($type == 'n') $chars = '0123456789';
else $chars = '0123456789';

$result = '';
for ($i = 0; $i < $len; $i ++){
$index = mt_rand(0, strlen($chars) - 1);
$result .= substr($chars, $index, 1);
}
return $result;
}

session_start();

/* 输出图片类型，字符长度，类型 */
$imgtype = 'gif';
$len = 4;
$vcodetype = 'n';

$width = 15 * $len;
$height = 24;
/* 生成随机字符串并写入SESSION */
$vcode = get_rand_string($len, $vcodetype);
$_SESSION['vcode'] = $vcode;
header("Content-type: image/".$imgtype);

if($imgtype != 'gif' && function_exists('imagecreatetruecolor')){
$im = imagecreatetruecolor($width, $height);
}else{
$im = imagecreate($width, $height);
}

$r = mt_rand(0, 255);
$g = mt_rand(0, 255);
$b = mt_rand(0, 255);
/* 生成背景颜色 */
$backColor = ImageColorAllocate($im, $r, $g, $b);
/* 生成边框颜色 */
$borderColor = ImageColorAllocate($im, 0, 0, 0);
/* 生成干扰点颜色 */
$pointColor = ImageColorAllocate($im, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));

/* 背景位置 */
imagefilledrectangle($im, 0, 0, $width - 1, $height - 1, $backColor);
/* 边框位置 */
imagerectangle($im, 0, 0, $width - 1, $height - 1, $borderColor);

/* 字符串颜色(背景反色) */
$stringColor = ImageColorAllocate($im, 255 - $r, 255 - $g, 255 - $b);

/* 产生干扰点 */
$pointNumber = mt_rand($len * 25, $len * 50);
for($i=0; $i<=$pointNumber; $i++){
$pointX = mt_rand(2,$width-2);
$pointY = mt_rand(2,$height-2);
imagesetpixel($im, $pointX, $pointY, $pointColor);
}

imagettftext($im, 15, 0, 4, 20, $stringColor, "Vera.ttf", $vcode);
$image_out = 'Image' . $imgtype;
$image_out($im);
@ImageDestroy($im);