Those of you running Windows 10 will be familiar with the regularly-changing "lockscreen" images showing things like beautiful scenery and scenes from nature:
https://www.tekrevue.com/tip/find-windows-spotlight-lock-screen-images-windo...
The last one I just saw was labelled "copyright [photographer name] and Shutterstock"
Is there someone at WMF, with contacts at Microsoft, who could persuade them to use some featured images from Commons, with a small piece of text explaining that people may upload their own images?
That would seem to be a simple way to do a massive piece of outreach, to a new audience.