Sorry if this is already been mentioned/discovered but you can take great screenshots in Witcher 3 w/out the UI showing using this "photo mode" mod/method:
http://www.gameranx.com/updates/id/28216/article/the-witcher-3-photo-mode-tool-allows-you-to-compose-fantastic-screenshots/ 

I wish someone would automate it into a one button press thing, but at least it works.

![Man it's such a beautiful game!][1]


  [1]: https://i.sstatic.net/2NWGg.jpg