在php中调整图像大小?不能让它工作

我有这个代码，我已经尝试创建，不知道我做错了什么。

    // SET ERROR FLAG
    $error = false;
    // MAKE SURE FILE IS AN IMAGE
    if (!list($width, $height) = getimagesize($_FILES['avatar']['tmp_name'])) {
        $error = true;
    } 
    // MAKE SURE FILE COMES FROM FORM
    if (!is_uploaded_file($_FILES['avatar']['tmp_name'])) {
        $error = true;
    }
    // MAKE SURE FILESIZE IS NOT OVER 1MB
    if (filesize($_FILES['avatar']['tmp_name']) > 1048576) {
        $error = true;
    }
    // TARGER TO SAVE FILE AND CHANGE FILENAME AND FILE TYPE
    $target = 'images/avatars/' . md5($user['id']) . '.gif';
    // IMAGE RATIO AND RESIZING
    $imgRatio = $width / $height;
    if ($imgRatio > 1) {
        $newWidth = 200;
        $newHeight = 200 / $imgRatio;
    } else {
        $newWidth = 200 * $imgRatio;
        $newHeight = 200;
    }
    $imgResized = imagecreatetruecolor($newWidth, $newHeight);
    $newImg = imagecreatefromgif($_FILES['avatar']['tmp_name']);
    $newImg = imagecopyresized($imgResized, $newImg, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
    // SUCCESSFULL IMAGE UPLOAD
    if (!$error && move_uploaded_file($newImg, $target)) {
        echo '<p>Your avatar was uploaded successfully.</p>';
        // ERROR UPLOADING IMAGE
    } else {
        echo '<p>There was an error uploading your avatar.</p>';
    }

它总是失败，我不能让调整大小的工作，甚至一个链接到一个好的教程就足够了，

新年快乐!