getting high resolution photos that were posted on a page wall/feed

I'm getting my page wall with the open graph. And when someone posted a photo, I get it on the JSON

{
     "id": "27888702146_10150369820322147",
     "from": {
        "name": "brocoli",
        "category": "Record label",
        "id": "27888702146"
     },
     "message": "Vincent Epplay / David Fenech / Jac Berrocal \u00e0 Beaubourg ce soir, 19h, gratos.",
     "picture": "http://photos-f.ak.fbcdn.net/hphotos-ak-snc7/305819_10150369820292147_27888702146_8255527_583491475_s.jpg",
     "link": "https://www.facebook.com/photo.php?fbid=10150369820292147&set=a.386279807146.165840.27888702146&type=1",
     "icon": "http://static.ak.fbcdn.net/rsrc.php/v1/yz/r/StEh3RhPvjk.gif",
     "type": "photo",
     "object_id": "10150369820292147",
     "created_time": "2011-10-16T08:22:21+0000",
     "updated_time": "2011-10-16T08:22:21+0000",
     "likes": {
        "data": [
           {
              "name": "brocoli",
              "category": "Record label",
              "id": "27888702146"
           },
           {
              "name": "Agathe Morier",
              "id": "601668526"
           }
        ],
        "count": 2
     },
     "comments": {
        "count": 0
     },
     "is_published": true
  }

The problem is that the picture link is a low resolution copy of the picture.

How can I get the URL of the full picture ?

Thanks!!

Best

Geoffroy