Thierry Volpiatto <thievol@posteo.net> writes:

> Don't know if you already added a command for xfce, if not here is what
> I use:
>
>     (apply #'call-process "xfconf-query" nil nil nil
>            `("-c"
>             "xfce4-desktop" "-p"
>             "/backdrop/screen0/monitoreDP/workspace0/last-image" "-s"
>             ,file))

I did not yet have the command, so thank you.  I have added this to
wallpaper.el on master now (commit fe7c015b20 or attached patch).

Do you mind testing to see if it works for you?