For example, this photo is only visibly by me,

http://www.facebook.com/photo.php?fbid=706480749906

You can see it if I give you the special link which skips the permission check,

http://www.facebook.com/photo.php?fbid=706480749906&l=a5...

Or on the CDN, which doesn't know about permissions,

http://a7.sphotos.ak.fbcdn.net/hphotos-ak-ash4/432125_706480...