I think that I have identified what I need to ask for.

I would like to understand if I can use an automatic pxe to store an
image on the image server of Zen.

If I do manually an img makep etc. etc. is all working but I do a

img auto

that's return an error because, I think, it try to retrieve an image
from the server to the workstation and not the inverse as I would like
to do.

Are the rules defined in the imaging server and related to unregistered
machines, used only to send images to the machines or can I also save
automatically the image of a machine not registered via pxe with a
rule? If so, where i need to define (and how) to do that?