//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
		 var respuesta = receiveReq.responseText;

		 if (respuesta == "OK") {
			 document.frmCaptcha.submit();
	 	 }
		 else if(respuesta == "KO") {
			 //Mostramos por pantalla el mensaje de error
			 document.getElementById('result').innerHTML = 'No introdujo el c&oacute;digo de seguridad correcto.<br>';
			 document.getElementById('result').innerHTML += 'Por favor int&eacute;ntelo de nuevo.';
			 
			//Regeneramos el código de seguridad
   			img = document.getElementById('imgCaptcha'); 			 
			img.src = 'create_image.php?' + Math.random();			
		 }
	}
}

//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);
}