I did this by clicking the icon at the top, pasting in the image URL and posting. It has not been working for me all morning, but it worked this time.
https://flic.kr/p/TbVnBr
.. well, it worked one time. Embedding an image seems to only work if you do it on your first pass on the post. If you try it in "edit" mode, it is not working. And, when I edited the post to add the text, the image disappeared.