如何使PHP不会裁剪到我调整大小的左上角

我正在用PHP将图像（用于用户的配置文件图标）调整为200x200大小，这样我就不会在页面上塞满巨大的图像。然而，如果不是正方形，我的代码似乎会裁剪以删除图像左上角以外的任何内容。如何将其正常调整为200x200？这是我的代码：

    <?php
//Function that will create a thumbnail of images submitted
function createThumbnail($image_name, $thumbnail_name, $size, $type) {
                //creates the image based on the type of file
                if($type == "image/jpeg") {
                    $image = imagecreatefromjpeg($image_name); 
                }
                else if ($type == "image/png") {
                    $image = imagecreatefrompng($image_name);
                }
                else if ($type == "image/gif") {
                    $image = imagecreatefromgif($image_name);
                }

                $thumbnail = imagecreatetruecolor($size, $size); 

                // if height and width are not equal... 
                if(imagesx($image) > imagesy($image)){
                    imagecopyresized($thumbnail, $image, 0, 0, 0, 0, 200, 200, imagesy($image), imagesy($image)); 
                }
                else {
                    imagecopyresized($thumbnail, $image, 0, 0, 0, 0, 200, 200, imagesx($image), imagesx($image)); 
                }

                if($type == "image/jpeg") {
                    imagejpeg($thumbnail, $thumbnail_name, 100);  
                }
                else if ($type == "image/png") {
                    imagepng($thumbnail, $thumbnail_name, 0); 
                }
                else if ($type == "image/gif") {
                    imagegif($thumbnail, $thumbnail_name); 
                }
}
    ?>

谢谢大家！-Adam