__________MAIN_PAGE__________

require 'general.php';

if(checkCaptch($_POST['captchaInput']){
    //Reload the page, allowing user to login
}
else{
    die("Captcha is wrong");
}

__________LOGIN_PAGE__________

require 'general.php';

function login(){
    $sUser = $_POST['nameInput'];
    $sPass = $_POST['passInput'];
    $bLoginCorrect = false;
    $bCaptchaCorrect = false;
    $sError = "";
    /*
    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    Check username and password in database, using valuable CPU and memory resources.
    if everything works out then $bLoginCorrect = true;
    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    */
    $bCaptchaCorrect = checkCaptch($_POST['captchaInput']);
    if($bLoginCorrect){
        if($bCaptchaCorrect){
            /*
            Yey login!
            Go to to user section
            */
        }
        else{
            $sError .= "Captcha is wrong. ";
        }
    }
    else{
        sError .= "Username/Password is wrong";
    }
    die(sError);
}

login();

__________GENERAL_PAGE__________(general.php)

$sCaptcha = getCurrentCaptcha();

function checkCaptch(){
    if($_POST['captchaInput'] == $sCaptcha){
        /*
        Set all cookies/db entries/whatever to show captcha entered correctly.
        However you are doing it right now, no changes are needed.
        */
        return true;
    }
    else{
        return false;
    }
}