I'm looking at teaching image-dired.el to set your desktop background.
Because A) this finishes a TODO that has been in that file for going on
15 years, and B) any respectable image viewer must know how to set your
desktop background.

However, this code is not really tied to image-dired.el; only one line
and the name of the defun ties it to that library.  For example, it
could be used in thumbs.el (that has similar capabilities), and it could
even be useful as a stand-alone command.

So I started thinking that just like the recently added gravatar.el,
perhaps we should put this stuff in a new library
lisp/image/desktop-background.el?

(Or some better name, suggestions welcome.)

Please see the attached tentative diff for image-dired.el to get an
idea.  (Please ignore the somewhat unwieldy defcustoms; I followed the
scheme in image-dired.el and intend to clean that up.)

Maybe this will even work automagically on other operating systems than
GNU/Linux, if the commands it uses has been ported to them.