Jerry is right, Photobucket has implemented a new plan for people who use their service for what they call "third party hosting", that is using your photos on forums etc.
They have went from a basically free service to charging $399. per year for sharing your photos.
Most everyone here has went to another photo hosting site such as Imgur. Some members have updated their old photobucket posts, but there is still many old photobucket pics out there that will come up like the one you show in your thumbnail.
Yup! These are the extensions I use myself. They work fine
Something makes me think the devs did the filtering this way on purpose... it's definitely possible to reroute the file without using any headers on the request... edit: maybe it isn't so easy now that I've dug through the source code. This same method will likely work with other websites so long as you understand how they filter by request...
If it's a request to photobucket, it will do the following:
-check to see if it's an image being linked to
-if it is, do the following:
--grab the user, and create a link to their full media folder
--find the referer property (what URL the request came from), and replace it with the link to that user's generic media folder
This works because they allow you to view any photos as long as you're navigating their site. There's no hotlinking restrictions within their own domain. So if you pretend you are from their own domain, they give it the OK.