I was thinking of reporting this as an error, but perhaps it was intentional.
Currently delta.chat does not display images embedded in an html message. I think in the end they are attachments, and they should be shown as such …
I am creating these messages with the Microsoft Outlook 2016 mail application
You are right, even if I check “Attatch image” in Thunderbird, DC still does not show it. (it could also be just a link to where in the internet the image is stored)