var source = 'abcdefghklmnprstuvwxyz0123456789'
var captcha = '';
var length = 5

function setCaptcha() {
	captcha = '';
	for (var i=0;i<length;i++) {
		captcha += source.charAt(Math.floor(Math.random()*source.length));
	}
}

function drawCaptcha() {
	if (captcha == '') setCaptcha();
	document.write("<div id='divCaptcha' class='divCaptcha'>");
	document.write("	<span id='spanCaptcha' class='spanCaptcha'>" + captcha + "</span>");
	document.write("	<input type='text' name='txtCaptcha' id='txtCaptcha' class='txtCaptcha' />");
	document.write("	<input type='button' name='btnCaptcha' id='btnCaptcha' class='btnCaptcha' value='Change' onclick='resetCaptcha()' />");
	document.write("</div>");
}

function resetCaptcha() {
	setCaptcha();
	document.getElementById('spanCaptcha').innerHTML = captcha;
}

function testCaptcha() {
	c = document.getElementById('txtCaptcha').value;
	return (c == captcha);
}