php验证码函数使用的例子

<script language="javascript">
/**
 * php 验证码函数应用举例
 * Edit www.jb200.com
*/
function _code($_code_length = 4, $_width = 75, $_height = 25){
for($i=0;$i<$_code_length;$i++){
$_nmsg .= dechex(mt_rand(0,15));
}
$_SESSION["code"] = $_nmsg;

$_img = imagecreatetruecolor($_width, $_height);
$_white = imagecolorallocate($_img, 250, 250, 250);
imagefill($_img, 0, 0, $_white);
$_gray = imagecolorallocate($_img, 196, 196, 196);
imagerectangle($_img, 0, 0, $_width-1, $_height-1, $_gray);

for ($i=0; $i < 6; $i++) {
$_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
imageline($_img, mt_rand(0,$_width), mt_rand(0, $_height),mt_rand(0,$_width), mt_rand(0, $_height), $_md_color);
}

for ($i=0; $i < 50; $i++) {
$_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255));
imagestring($_img, 1, mt_rand(1,$_width-5), mt_rand(1, $_height-5), "*", $_md_color);
}

for ($i=0; $i < $_code_length ; $i++) {
$_md_color = imagecolorallocate($_img, mt_rand(0,102), mt_rand(0,102), mt_rand(0,102));
imagestring($_img, 5, $i * $_width/$_code_length+ mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION["code"][$i], $_md_color);
}

header("Content-Type:image/png");

imagepng($_img);
imagedestroy($_img);
}
</script>