将facebook个人资料与文本和图像合并

我正在尝试为Facebook创建一个应用程序，将用户的个人资料图像与背景图像和用户名称合并。这张图片是对那些成功回答测验的人的奖励。

这是用户提交答案后收到的页面上的相关代码：

        if ( $totalCorrect == 10) {
        echo "Congrats!";
            echo "<div id='results'>$totalCorrect / 10 correct</div>";

        echo '<img src="image.php">';
        ?> 

这是image.php 中的代码

<?php
// Create image instances


$im = imagecreatefromjpeg('xxx.jpg');

$black = ImageColorAllocate($im, 0, 0, 0); 


//The canvas's (0,0) position is the upper left corner 
//So this is how far down and to the right the text should start 
$start_x = 200; 
$start_y = 20; 
$font = 'arial.ttf';

Imagettftext($im, 12, 0, $start_x, $start_y, $black, $font, 'text to write'); 
$url = "http://graph.facebook.com/".$user_profile. "/picture";

$dest = imagecreatefromjpeg($url);
// Copy and merge
imagecopymerge($im, $dest, 10, 10, 0, 0, 180, 180, 100);

//Creates the jpeg image and sends it to the browser 
//100 is the jpeg quality percentage 
// Output and free from memory
header('Content-Type: image/jpg');
imagejpeg($im);

imagedestroy($dest);
imagedestroy($src);
?>

如果我把$url换成一个静态图像，代码就可以工作，但当我试图获取用户的配置文件时就不行了。有什么建议吗？谢谢你！