Images deployed as an artifact should have "image/xxx" as its content-type

I am considering to post images in artifacts to issue or pull-request.
I have found that expiring_download_url can be accessed publicly but its content-type is octet-stream. GitHub cannot treat octet-stream as image so markdown’s image-embedding syntax does not work.

Expiration of the public url does not matter. (GitHub server downloads and starts mirroring the image when the comment was posted)