var ajaxformobj;
function getXmlHttpRequestObject() {
 if (window.XMLHttpRequest) {
  return new XMLHttpRequest(); //Mozilla, Safari ...
 } else if (window.ActiveXObject) {
  return new ActiveXObject("Microsoft.XMLHTTP"); //IE
 } else {
  alert("Your browser doesn't support the XmlHttpRequest object.");
 }
}
var receiveReq = getXmlHttpRequestObject();

function makeRequest(url, param) {
 if (receiveReq.readyState == 4 || receiveReq.readyState == 0) {
  receiveReq.open("POST", url, true);
  receiveReq.onreadystatechange = updatePage;
  receiveReq.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  receiveReq.setRequestHeader("Content-length", param.length);
  receiveReq.setRequestHeader("Connection", "close");
  receiveReq.send(param);
 }   
}
function updatePage() {
 if(receiveReq.readyState!=4)
 {
  document.getElementById("check").innerHTML="checking.....";
 }
 if (receiveReq.readyState == 4) {
  document.getElementById("check").innerHTML="";
  var result = receiveReq.responseText;  
  if(result!="1") {
   alert("Please enter valid Verification Code.");
   ajaxformobj.txtcode.focus();
   img = document.getElementById('imgCaptcha'); 
   img.src = 'create_image.php?' + Math.random();
   return false;
  } else{
   ajaxformobj.submit();
  }
 }
}
function getParam(theForm) { 
 ajaxformobj = theForm;
 var url = 'captcha.php';
 var postStr = theForm.txtcode.name + "=" + encodeURIComponent(theForm.txtcode.value);
 makeRequest(url, postStr);
}