Hi Ian,
It's not duplicated issue, you accidentally set to show images twice there.
With being said, in the module settings of Zentools 2 module, you set to show Image + Intro text of article which both have image.
I just updated in that article by adding a readmore button so it can separate intro text and full text.
And add image into Image & Link tab of article: https://prnt.sc/sg34u1
This is default behavior for creating a Joomla article. For the new article, pls add the same way.
Regards