javascript generated captcha and javascript captcha validation in my university website... over hundred thousand students use this website to check results

function ValidCaptcha(){
var string1 = removeSpaces(document.getElementById("AVCODE").value);
var string2 = removeSpaces(document.getElementById("UVCODE").value);
if (string1 == string2){
return true;
}
else{
alert("invalid captcha");
return false;
}
}
function removeSpaces(string){
return string.split(' ').join('');
}