var capcheck=false;
//Gets the browser specific XmlHttpRequest Object
function getXmlHttpRequestObject()
{
 if (window.XMLHttpRequest)
 {
    return new XMLHttpRequest(); //Mozilla, Safari ...
 } else if (window.ActiveXObject) {
    return new ActiveXObject("Microsoft.XMLHTTP"); //IE
 } else {
    //Display our error message
    alert("Your browser doesn't support the XmlHttpRequest object.");
 }
}

//Our XmlHttpRequest object
var receiveReq = getXmlHttpRequestObject();

//Initiate the AJAX request
function makeRequest(url, param) {
//If our readystate is either not started or finished, initiate a new request
 if (receiveReq.readyState == 4 || receiveReq.readyState == 0) {
   //Set up the connection to captcha_test.html. True sets the request to asyncronous(default) 
   receiveReq.open("POST", url, true);
   //Set the function that will be called when the XmlHttpRequest objects state changes
   receiveReq.onreadystatechange = updatePage; 

   //Add HTTP headers to the request
   receiveReq.setRequestHeader("Content-type","application/x-www-form-urlencoded");
   receiveReq.setRequestHeader("Content-length", param.length);
   receiveReq.setRequestHeader("Connection", "close");

   //Make the request
   receiveReq.send(param);
 }   
}

//Called every time our XmlHttpRequest objects state changes
function updatePage()
{
 //Check if our response is ready
 if (receiveReq.readyState == 4)
 {
   //Set the content of the DIV element with the response text
   //document.getElementById('result').innerHTML = receiveReq.responseText;
   var retvalue = receiveReq.responseText;
   if(retvalue=="false")
   {
   document.getElementById('result').innerHTML = "Invalid Security Code. Please try again";
   document.getElementById("butSubmit").disabled = true;
   capcheck = false;
   //Get a reference to CAPTCHA image
   img = document.getElementById('imgCaptcha'); 
   //Change the image
   img.src = 'createimage.php?' + Math.random();
   }
   else if(retvalue=="true")
   {
   //document.getElementById('result').innerHTML = receiveReq.responseText;
   document.getElementById('result').innerHTML = " ";
   document.getElementById("butSubmit").disabled = false;
   capcheck = true;
   }
 }
}

//Called every time when form is perfomed
function getParam(theForm)
{
 //Set the URL
 var url = 'captcha.php';
 //Set up the parameters of our AJAX call
 var postStr = theForm.txtCaptcha.name + "=" + encodeURIComponent(theForm.txtCaptcha.value );
 //Call the function that initiate the AJAX request
 makeRequest(url, postStr);
}