Until either image uploads or an embed method for a Link Post that is an image, the (interim) method is to create a Discussion post and then use the markdown for displaying an Image. Described in this post:
There's also a nuance with the upload sites. For a link from a site like Imgur, or Postimages.org, ... the link to the image itself would be what is used. For example, the Imgur link for an upload (e.g., https://imgur.com/a/tcCorJh) won't work, but the link directly to that upload's jpg image (e.g., https://i.imgur.com/NxhUIBJ.jpeg ) will work.
