When you upload your pictures into photobucket, copy the url address in the Direct Link field just below the photo. Using the IMG Code field in photobucket won't work as hn.com uses different tags when inserting photos.
Then when you are making your post in hn.com; click the image button... it will insert into your post. Then just paste the link in between the two tags.
Your text will end up with something like
(minus the **). This will insert your photo into the post.
Good luck