title: Get user profile picture by Id
body: <p>I'm now working on a web application which is mostly based of facebook graph api.
  I hold some data about users - actually , the possible public data available - such as name and id.
  I also know that a profile picture is a part of the public data, and I wondered how I'll be able to get a direct link to a profile picture of a user only by using his id?</p>
  
  <p>Thanks in advance</p>