The IMG link should work automatically. I normally don't work with Photobucket, but what type of permissions do you have set? Reason I ask is because certain restrictions will give you a URL that begins HTTPS instead of just HTTP. HTTPS pictures do not post here I've learned.
Post a link and I'll see if I can figure it out for you. If not, I know a few people to ask who post using Photobucket. I've fixed a few for some people in the past. Once I figure out the problem, I'll teach you how to do it.