在脸书墙上张贴图片

我可以在消息内的墙上发布图片有任何限制吗？

当我使用这个代码：

if (isset($_GET['publish'])){
        try {
            $publishStream = $facebook->api("/$user/feed", 'post', array(
                'message' => "I love thinkdiff.net for facebook app development tutorials. <img src="http://c3354688.r88.cf0.rackcdn.com/wp-includes/images/smilies/icon_smile.gif" alt=":)" class="wp-smiley"> ",
                'link'    => 'http://ithinkdiff.net',
                'picture' => 'http://thinkdiff.net/ithinkdiff.png',
                'name'    => 'iOS Apps & Games',
                'description'=> 'Checkout iOS apps and games from iThinkdiff.net. I found some of them are just awesome!'
                )
            );
            //as $_GET['publish'] is set so remove it by redirecting user to the base url
        } catch (FacebookApiException $e) {
            d($e);
        }
    }

一切都很好，但如果我把图片换成不同的URL，尽管图片是可用的。

有什么建议吗？