var request = null;

function createRequest() {
	try {
		request = new XMLHttpRequest();
	} catch (trymicrosoft) {
		try {
			request = new ActiveXObject("Msxml2.XMLHTTP");
		} catch (othermicrosoft) {
			try {
				request = new ActiveXObject("Microsoft.XMLHTTP");
			} catch (failed) {
				request = null;
			}  
		}
	}
	if (request == null)
		alert("Nie udało się utworzyć obiektu żądania!");
}

function refresh_captcha() {
	createRequest();
	var url = "captcha-refresh";
	request.open("GET", url, true);
	request.onreadystatechange = updatePage;
	request.send();
}

function updatePage() {
	if (request.readyState == 4) { 
		img = document.getElementById('captcha_img');
		img.src = 'images/captcha.jpg?' + Math.random();
	}
}