Earlier there were hacks to see the pictures of user from their private albums, even if you did not have access. But facebook has sealed most, if not all those vulnerabilities, that possibly is a threat to their users privacy.
However, there are still ways you can see some pictures, which are available to the rest of the world and the user not being in your list.
Lets suppose you you receive a picture of someone and you are curious to see the rest of the pictures in that particular album. You can do that using the file name to do so.
The architecture is the same to store all the photos in the facebook. The pictures are stored as two groups of <number>.
Something like photo.php?id=XXX&pid=XXX where the first number is the facebook id of the owner and the second number is the image/album id.
You can use look into pictures of only those albums whose privacy setting is set to public. You’ll also be able to navigate through the albums :).
Let me know in the comment section if you want to know more about how to hack into the facebooks system … not for everyone though 😛
All in all, we should remember that facebook, is not a small organization and they have one of the biggest user base on the Internet and those users are their asset which they can’t afford to loose. I don’t mean to say, hackers will never find a way to hack into private album features. But Facebook is vigilant enough to track and close those vulnerabilities as and when they are found.
For those who came here looking for a hack to view private albums on facebook, I’m sorry I don’t know any that work now, though at some point I did know