php 验证码

$num=4;
$w=135;
$h=40;
$code = "";
for ($i = 0; $i < $num; $i++) {
$code .= rand(0, 9);
}
//4位验证码也可以用rand(1000,9999)直接生成
//将生成的验证码写入session，备验证时用
sesstion_start();                // 首先开启session
$_SESSION['yzm'] = $code;
//创建图片，定义颜色值
header("Content-type: image/PNG");
$im = imagecreate($w, $h);
$black = imagecolorallocate($im, 0, 0, 0);
$gray = imagecolorallocate($im, 200, 200, 200);
$bgcolor = imagecolorallocate($im, 255, 255, 255);
//填充背景
imagefill($im, 0, 0, $gray);

//画边框
imagerectangle($im, 0, 0, $w-1, $h-1, $black);

//随机绘制两条虚线，起干扰作用
$style = array ($black,$black,$black,$black,$black,
$gray,$gray,$gray,$gray,$gray
);
imagesetstyle($im, $style);
$y1 = rand(0, $h);
$y2 = rand(0, $h);
$y3 = rand(0, $h);
$y4 = rand(0, $h);
imageline($im, 0, $y1, $w, $y3, IMG_COLOR_STYLED);
imageline($im, 0, $y2, $w, $y4, IMG_COLOR_STYLED);

//在画布上随机生成大量黑点，起干扰作用;
for ($i = 0; $i < 50; $i++) {
imagesetpixel($im, rand(0, $w), rand(0, $h), $black);
}
//将数字随机显示在画布上,字符的水平间距和位置都按一定波动范围随机生成
$strx = rand(20, 40);
for ($i = 0; $i < $num; $i++) {
$strpos = rand(1, 6);
imagestring($im, 5, $strx, $strpos, substr($code, $i, 1), $black);
$strx += rand(8, 12);
}
imagepng($im);//输出图片
imagedestroy($im);//释放图片所占内存

$("#getcode_num").click(function(){
$(this).attr("src",'index.php?r=index/code&=' + Math.random());
});