I currently use the follow script to Auto Upload (external) images embedded in bbpress topics & replies to my Media library:
[login to view URL]
It works GREAT.
Unfortunately, in order to get the images to upload (for existing posts) the script forces the user to click on Topics, highlight them, click edit and then click update BEFORE it will save the images in the Media files.
I have imported several Thousand topics & replies into my forums.
It will need brief timeouts every 100 requests to prevent server overload.
PS. I have a MASTER SRC copy of the files with ALL the GitHub Pull Requests & Fixes implemented that I can provide to the coder/developer to save time.