I also use PhotoBucket. After uploading your image to Photobucket, select your photo from the library and, in the options on the right, select "Direct". This puts a link into your clipboard.
Back in your forum post edit section section "insert image". I use the "url" option, deselect the "Retrieve file..." and paste the link into the edit box. It's always worth going to the Advanced edit view so you can view your post in progress in case it doesn't work.
The images are not stored in the forum so if you remove your image from Photobucket the link will show as broken.
Photobucket can be very slow at times.