[klibertp]

You cannot embed images in Org documents. Or rather, you can, but would need to code the support for this for yourself. On the other hand, displaying images within the Org documents is trivial. You just need to have the image file saved somewhere. Then you insert a link to the image file and, with the default settings, you should be able to see the image rendered inline in the document. You can also generate the image from within the document. You write a ditaa code block, execute it, and the png with your UML (or whatever) is inserted or updated.

On the other hand: no, Emacs is not a WYSIWYG word processor. The need to support terminal as a display backend weights heavily on the pace of GUI improvements. That's because all interface elements need to be renderable on all backends (not strictly true, but the prejudice against GUI-only elements is significant). So if you hope to be able to easily and conveniently display something like this: https://klibert.pl/statics/vw-doc-view.png then Emacs is empathically not the best tool for the job.