Jquery Captcha validation plugin

Verify.php
 ////////////
<?php
 require_once('recaptchalib.php');
 $privatekey = "6LcmKu8SAAAAAGE8er5WjsiuRWOyqNMfyk-QZiIj";
 $resp = recaptcha_check_answer ($privatekey,
                                 $_SERVER["REMOTE_ADDR"],
                                 $_GET["recaptcha_challenge_field"],
                                 $_GET["recaptcha_response_field"]);
// echo $privatekey.' '. $_SERVER["REMOTE_ADDR"].' challenge:'.$_GET["recaptcha_challenge_field"].' response:'.$_GET["recaptcha_response_field"];
 if (!$resp->is_valid) {
   // What happens when the CAPTCHA was entered incorrectly
  echo("false");
 } else {
   // Your code here to handle a successful verification
   echo("true");
 }
 ?>

js code in valdiation plugin

recaptcha_response_field:{
                    required: true,
                    remote: "Captcha/verify.php?recaptcha_challenge_field="+$('#recaptcha_challenge_field').val()