Answer by Sahil Mittal for Graph API new feed post object-Attachment not showing

I am assuming user gave the permission for user_photos / friends_photos. Since you have the photo_id, you may try this.

$pic = $facebook->api("/PHOTO_ID");$pic_url = $pic->source;$attachment =  array('access_token' => USER_ACCESS_TOKEN,'message'      => "...",'caption'      => "...",'name'         => "...",'description'  => "...",'link'         => URL,'picture'      => $pic_url);

ADDED

You need to store the image some where locally ,in a local server . due to this article