Facebook photos accessible without login, a feature or a bug?

I just was browsing my friends photos and accidentally right clicked on Firefox, I happened to click the copy image location. This image url when pasted in a browser was now available for anybody to see without logging in. So all a person has to do is copy those url's and expose it, anybody could see it. I think this is a bug considering the hosting of photos in a gated social network should be private. It would be ridiculous if this were a feature.

Comments?