I found a plugin that should let you add an image to the forum which will then be hosted on Imgur. You should be able to drag and drop images into the comment field and some code will be generated automatically. See below. Alternately, you can add multiple images with the Add Images
It does look like you can't edit a comment and add images after the fact. You should be able to edit original discussion posts though.
One big caveat, currently it doesn't work very well on mobile. If you're posting from a phone or other smaller mobile device you need to force the browser to give you the desktop version of the site. (Thanks to Open for the heads up)
So as many of you have noticed it's kind of a pain in the ass to post images right now. The big problem is that two of the major image repositories that most of us use (Google and OneDrive) have changed their architecture and no longer allow direct linking to images.
Baring a change in those policies (something that at least Microsoft is working on: https://onedrive.uservoice.com/forums/262982-onedrive/suggestions/8437309-bring-back-static-urls-for-image-files-currently
) we're stuck using other image hosts.
So far we can link from:
Photobucket (you need to select the direct link when you share an image)
Tinypic (you need to select the direct link when you share an image)
Imgur (open the image in a new window/tab and copy the URL address)
Flickr (This is using the embed code. It might not be optimum and it could be effected by the license the image was posted under.)
Facebook (open image in new tab/window can copy the URL address)
With regards to posting pics from mobile I'm not sure there is a great solution at this time. I think a few of the above mentioned hosting options have an app and you might be able to do it from there but YMMV.