All:
I've just uploaded a simple command line program that lets you do a screen grab from a Rigol DS1054Z 'scope[\*]. Confirmed to run on macOS, quite possibly runs under Linux and Windows (maybe one of y'all could test it for me!).
Start here for overview:
https://hackaday.io/project/164447-rigol-screen-grabber and/or go directly here for the code:
https://github.com/rdpoor/rigol-grabHere's a sample output:
[\*] PS: It may well work on other Rigol scopes, but that's not yet been tested.