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