session_start();
$GtSdk = new GeetestLib();
if ($_SESSION['gtserver'] == 1) {
    $result = $GtSdk->validate($_POST['geetest_challenge'], $_POST['geetest_validate'], $_POST['geetest_seccode']);
    if ($result == TRUE) {
        echo 'Yes!';
    } else {
        if ($result == FALSE) {
            echo 'No';
        } else {
            echo 'FORBIDDEN';
        }
    }
} else {
    $validate = $_POST['geetest_validate'];
    if ($validate) {
        $value = explode("_", $validate);
        $challenge = $_SESSION['challenge'];
        $ans = $GtSdk->decode_response($challenge, $value['0']);
        $bg_idx = $GtSdk->decode_response($challenge, $value['1']);
        $grp_idx = $GtSdk->decode_response($challenge, $value['2']);
        $x_pos = $GtSdk->get_failback_pic_ans($bg_idx, $grp_idx);
        if (abs($ans - $x_pos) < 4) {
            echo "yes";
        } else {
            echo "no";
        }
    } else {
        echo "no";
    }
}