[oe] meta-xfce: how to change the default background?

[California Sullivan]

Hi all,

When building an image and using the xfce package, I would like to be able
to set a custom default background (i.e., before the image is ever booted
up).

I have been unable to find any documentation on how to do this, and I
haven't found any clues by poking around in the layer.

Any pointers from somebody with experience in this area, or any links to
documentation on how this could be done would be very much appreciated.

Thank you,
Cal Sullivan