php 验证码

生成验证码代码如下：

public function captcha()
{
//初始化
$border      = 1;
$how         = 4;
$w           = 117;
$h           = 42;
$y           = 29;
$fontsize    = 18;
$alpha       = "abcdefghjkmnpqrstuvwxyz";
$number      = "23456789";
$captchacode = "";
srand((double)microtime()*1000000);
$font = VAR_PATH . "font/arialbd.ttf";

$img = imagecreate($w, $h);
//绘制基本框架
$bgcolor = imagecolorallocate($img, 247, 255, 236);
imagefill($img, 0, 0, $bgcolor);
if ($border) {
$black = imagecolorallocate($img, 204, 204, 204);
imagerectangle($img, 0, 0, $w-1, $h-1, $black);
}

//逐位产生随机字符
$j = 0;
for ($i = 0; $i < $how; $i++) {
$alpha_or_number = mt_rand(0, 1);
$str             = $alpha_or_number ? $alpha : $number;
$which           = mt_rand(0, strlen($str)-1);
$code            = substr($str, $which, 1);
$j               = !$i ? 15 : $j+25;
$color3          = imagecolorallocate($img, 87, 123, 35);
imagettftext($img, $fontsize, 0, $j, $y, $color3, $font, $code);
//imagechar($img, $fontsize, $j, $y, $code, $color3);
$captchacode .= $code;
}

//绘背景干扰线
/*
for ($i=0; $i<10; $i++) {
$color1 = imagecolorallocate($img, mt_rand(0,255), mt_rand(0,255), mt_rand(0,255));
imagearc($img, mt_rand(-5,$w), mt_rand(-5,$h), mt_rand(20,300), mt_rand(20,200), 55, 44, $color1);
}
*/

$_SESSION['captchacode'] = $captchacode;
header("Content-type: image/gif");
imagegif ($img);
imagedestroy($img);
exit;
}

验证码显示html区域

<div class="field">
<label>验证码</label>
<div class="input-box">
<input type="text" class="input-text required" name="captcha" style="width:197px;" />
<img src="<?php echo $this->getUrl('index/index/captcha'); ?>" οnclick="this.src=this.src+'?';" title="点击刷新验证码"  style="cursor:pointer;" />
</div>
</div>