Theres two ways of doing it. Underneath each pic in your photobucket album are three lines. One says Url, the next says Tag and the bottom says Img. Copy all of the text from the Img box and paste that into your post and once you post the reply you will get the picture come up in your post (In the reply box it will just be a line of text but you will get the picture in the post)
The second is to click on the picture in your photobucket album that you want to post so that it opens into a full size picture then right click on the open picture, click copy then paste this into your post (This way you see the picture in the reply box).