//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 {
        alert("Your browser doesn't support the XmlHttpRequest object.");
    }
}


var receiveReq = getXmlHttpRequestObject();
var myURL;
var myRandomString;
var ctlName;


function makeRequest(url) { 
    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("Connection", "close");
        receiveReq.send(null);
    }   
}


function updatePage() {
    if (receiveReq.readyState == 4) {
        document.getElementById('imgCaptcha').value = myRandomString;
        img = document.getElementById('imgCaptcha'); 
        
        img.src = myURL + '&' + Math.random();
    }
}


function getParam(img) {
    //ctlName = img.replace('imgCaptcha', '');
    var myRandomString = randomString();
    var url = '../MediaCenter/JpegImage.aspx?captcha=' + myRandomString;

    myURL = url;
    makeRequest(url);
}

function randomString() {
	var chars = "abcdefghjkmnpqrstuvwxyz2346789";
	var string_length = 4;
	var randomstring = '';
	
	for (var i=0; i<string_length; i++) {
		var rnum = Math.floor(Math.random() * chars.length);
		randomstring += chars.substring(rnum,rnum+1);
	}
	
	return randomstring;
}