Just learned you can create QR codes pretty easily in LibreOffice:
It inserts an object in the document at that point, so it can be resized and moved around. It is not an image that can be exported separately from the document (or at least, I have not found out how to do so yet). This worked OK for my needs, though, which was creating a PDF document with some QR codes in it.
Via help.libreoffice.org page