The Nintex Document Generation action is amazing, to be able to create rich and dynamic documents from data in your workflow. What has come recently, is if there was a way to take an image file, that was attached to a List Item, and add that to the document also.
Well............ (wait for it)........... there is!! Surprised?? :)
In the above video, I walk thought how to do something like this. Granted, I didn't exactly make the document template look nice, but I have no artistic skills. At least you can see that it's possible.
The idea is to have the Nintex Workflow make a REST call to SharePoint, to find the URL to the attachment, before plopping it into the Document Generation action. The REST call and pulling out the data from the dictionary is the hard part. But once you've done that, the rest is super easy.
I've attached the workflow below. You'll need to modify it, to change the URL a little and have your own Document Template..... but that's it. Then you should be up and running.