It depends where you want the picture to show up. If you want the photobucket picture to just appear in the body of a thread, you use the <tag> code. Just copy and paste it from photobucket. It will show up as the html address when you are typing your reply, but it will show up as a picture after you add your reply.

If you want the picture to show up in your signature, you use the [IMG] code.

If you want it to show up as an avatar, you have to be sure that it is in JPEG format.