var length = 3;
var form = document.forms['captchaform'];
var captchaMsg = document.getElementById('captchacode');

function stopEnterKey(evt) {
  var evt = (evt) ? evt : ((event) ? event : null);
  var node = (evt.target) ? evt.target : ((evt.srcElement) ? evt.srcElement : null);
  if ((evt.keyCode == 13) && (node.type=="text"))  {return false;}
}

form.onkeypress = stopEnterKey; 

var alphaNum = new Array(36);
var index;
var captchaString = '';
var randomNum;
for (index = 0; index < alphaNum.length; index++) {
	if(index < 10)
		alphaNum[index] = '' + index; //fill numbers
	else
		alphaNum[index] = String.fromCharCode(index - 10 + 97); //fill letters 
}

for (index = 0; index < length; index++) {
	randomNum = Math.round(Math.random() * (alphaNum.length - 1));
	captchaString += alphaNum[randomNum];
	captchaMsg.innerHTML += '<img src="http://goldranking.com/captcha/' + alphaNum[randomNum] + '.gif" />';
}

function validateForm() {
	var captchaRsp = document.getElementsByName('captcharesponse')[0].value.toUpperCase();
	if (captchaRsp == captchaString.toUpperCase())
		form.submit();
	else
		alert("The characters you entered did not match. Please try again.");
}