Via the RTE and the "Insert Image" button. Using the external image URL tab. I doesn't work when I try doing it in this forum either.
This is what you get if you try via the RTE.
I found if you add the ASHX extension to the FileViewers section in the communityserver.config you can get it to appear in the RTE as a preview. However when you post it still gets stripped.
snopow0412.ashx?mw=465