function _recaptcha_http_post($host, $path, $data, $port = 80) {
$req = _recaptcha_qsencode ($data);
$response = '';
$url = $host.$path;
$post_data = $req;
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
// 我们在POST数据哦！
curl_setopt($ch, CURLOPT_POST, 1);
// 把post的变量加上
curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);
$output = curl_exec($ch);
curl_close($ch);
//echo $output;
$response = $output;
return $response;
}
function recaptcha_check_answer ($privkey, $remoteip, $challenge, $response, $extra_params = array())
{
if ($privkey == null || $privkey == '') {
die ("To use reCAPTCHA you must get an API key from <a href='https://www.google.com/recaptcha/admin/create'>https://www.google.com/recaptcha/admin/create</a>");
}
if ($remoteip == null || $remoteip == '') {
die ("For security reasons, you must pass the remote ip to reCAPTCHA");
}
//discard spam submissions
if ($challenge == null || strlen($challenge) == 0 || $response == null || strlen($response) == 0) {
$recaptcha_response = new ReCaptchaResponse();
$recaptcha_response->is_valid = false;
$recaptcha_response->error = 'incorrect-captcha-sol';
return $recaptcha_response;
}
$response = _recaptcha_http_post (RECAPTCHA_VERIFY_SERVER, "/recaptcha/api/verify",
array (
'privatekey' => $privkey,
'remoteip' => $remoteip,
'challenge' => $challenge,
'response' => $response
) + $extra_params
);
$answers = explode ("\n", $response [1]);
$recaptcha_response = new ReCaptchaResponse();
$pos = strpos($response, 'true');
if ($pos === false) {
$recaptcha_response->is_valid = false;
$recaptcha_response->error = $response;
} else {
$recaptcha_response->is_valid = true;
}
return $recaptcha_response;
}

<html>
<body>
<form action="" method="post">
<?php
require_once('recaptchalib.php');
// Get a key from https://www.google.com/recaptcha/admin/create
$publickey = "你的公共key ---自己去http://www.google.com/recaptcha申请";
$privatekey = "你的私有key ---自己去http://www.google.com/recaptcha申请";
# the response from reCAPTCHA
$resp = null;
# the error code from reCAPTCHA, if any
$error = null;
# was there a reCAPTCHA response?
if ($_POST["recaptcha_response_field"]) {
$resp = recaptcha_check_answer ($privatekey,
$_SERVER["REMOTE_ADDR"],
$_POST["recaptcha_challenge_field"],
$_POST["recaptcha_response_field"]);
if ($resp->is_valid) {
echo "You got it!";
} else {
# set the error code so that we can display it
$error = $resp->error;
echo $error;
//echo $_POST["recaptcha_challenge_field"];
//echo $_POST["recaptcha_response_field"];
}
}
echo recaptcha_get_html($publickey, $error);
?>
<br/>
<input type="submit" value="submit" />
</form>
</body>
</html>