I am getting an image from facebook by the URL: http://external.ak.fbcdn.net/safe_image.php?d=d282e1e7c86c9270232f97ddc737df39&w=90&h=90&url=http%3A%2F%2Fi52.tin
Generally if you want to collect the profile pic of a user or page, the format for the icon size picture is:
http://graph.facebook.com/[page id/profile id]/picture
and for the large picture:
http://graph.facebook.com/[page id/profile id]/picture?type=large
EDIT Points to note: If the image stored on the facebook servers is less than the 200*200 dimensions, you would get the image as the highest resolution avaiable eg: 128*160. Either you can resize it using the GD library.
AND ONE MORE THING
Facebook supports 200*600px as the highest resolution for the profile pic. It will resize an image to fit into these dimensions by maintaining the aspect ratio.
*UPDATE as on 19th Feb, 2017 *
We need to use this new URL formation to get a desired profile image.
http://graph.facebook.com/{profile_id}/picture?width={number}&height={number}
[Thank you https://stackoverflow.com/users/2829128/vay]