Just copy/paste the image address from the top of your browser, from another window.. then come back to edit your first post.. and either paste between the image tags or use the icon that looks like a framed picture of a mountain. Don't forget to get rid of the 'http://' if you paste the full link when using the icon.
If you can't get the url directly from the image in photobucket... then once you're looking at the full size picture, right-click on the image and do Properties. It'll show you the image address. You can highlight that and right-click and choose copy, then come back and paste in your post.
a black car.