When you have brought the Photobucket image in question to the fore, ie, if you first have to choose one of the photos from your library, you will then be presented with the one image and four links to the lower right under Share Links.
If you just click over the link to the right of Image, the URL will disappear to be replaced by Copied.
You can then just Paste that directly into your Forum text box in the threads and you are done. This method removes the necessity to mess about with the IMG tags as explained above.