在PHP SDK中获取Photo_ID

How do i get the Photo_ID from an photo which my app uploaded with the PHP SDK Code:

$facebook->setFileUploadSupport(true);
$img = '/tmp/mypic.png';
$photo = $facebook->api(‘/me/photos’, ‘POST’,
                        array( ‘source’ => ‘@’ . $img,
                               ‘message’ => ‘Photo uploaded via the PHP SDK!’
                       ));

Didnt see that it will give any response.

The response of a successful upload is the id of the photo, example:

{
   "id": "1001207389476"
}

So $photo should hold a similar value.