function checkCaptcha(recaptcha_challenge_field,recaptcha_response_field) {
 var xmlHttp;
  try
    {
    // Firefox, Opera 8.0+, Safari
    xmlHttp=new XMLHttpRequest();
    }
  catch (e)
    {
    // Internet Explorer
    try
      {
      xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
      }
    catch (e)
      {
      try
        {
        xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
      catch (e)
        {
        alert("Your browser does not support AJAX!");
        return false;
        }
      }
    }
	
 	xmlHttp.open('get', 'captcha_challange.php?recaptcha_challenge_field='+recaptcha_challenge_field+'&recaptcha_response_field='+recaptcha_response_field, false);
  	xmlHttp.send(null);  // synchronous; returns when response is complete
	
	return xmlHttp.responseText;
}