This feature has bee replace by the Photo Chooser app.
When you view your photo album on Photobucket you'll see a "Feed for this Album" link on the bottom left of the page (red circle in the above photo).
Right click on that link and copy it. Then embed into the "Photo Album RSS link" box when you add a new photo.
Photobucket seems to have switched all customers to their beta site and that site doesn't offer the RSS sharing option. Hopefully they'll add it soon.