http://graph.facebook.com/{user_id or page_id}?fields=cover

{
  "cover": {
    "id": "XXX",
    "source": "https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-ash4/311205_989690200741_1231438675_n.jpg",
    "offset_y": 66
  },
  "id": "XXXXXX"
}

SELECT pic_cover FROM user WHERE uid='yourUserId'

[
 {
  "pic_cover": {
   "cover_id": someId,
   "source": "someUrl",
   "offset_y": someOffset
  }
 }
]

$albums = $facebook->api("/me/albums");
$album_id = "";
foreach($albums["data"] as $item){
//echo $item["id"]." - ".$item["name"]." - ".$item["type"]." - ".$item["cover_photo"]."<br/>";
    if($item["type"] == "profile"){
        $album_id = $item["id"];
    $profile_picture_id = $item["cover_photo"];
    break;
    }
}

{
  "cover": {
    "id": "XXX",
    "source": "https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-ash4/311205_989690200741_1231438675_n.jpg",
    "offset_y": 66
  },
  "id": "XXXXXX"
}

$json = file_get_contents("https://graph.facebook.com/PROFILE_ID?fields=cover");
$obj = json_decode($json);
echo $obj->cover ->source;