Pretty much any of it. If there's a photo I want a friend of mine to see, but they don't have permission to see it, I just send them the URL of the static content and it works every time, whether or not they're logged in.
https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc4/148199_...
Just for reference the picture should be this:
Oh ... the way I uploaded that to imgur? Using that URL above, so clearly that is wide open to the world.
Also, there is no restriction on who can see pictures when you a direct link to an image. This is mostly due to the fact that CDNs used to store static files usually don't send cookies and thus have no concept of a session.
I am familiar with what is in the URL, and I am also familiar with CDN's. I was merely posting my rebuttal to the OP who said it was obfuscated.