"Scanner" app on apples often come up with no way to save the scanned
image to af file.  This has been reported on a lot of forums, and the
solution is especially obscure: When it happens, the tool bar on  the
right  usually  has a "Use Custom Size" item.  Uncheck it.  This will
cause the image to be saved.

You might first want to fill in the "Name:" field, because  otherwise
you won't know where it was saved. It will be somewhere on your disk,
but Scanner won't tell you its name.

Yes, this is one of the worst "designs" anyone has ever seen. So much
for the vaunted Apple user-friendliness image.

Note that there's no button or menu item to tell it to save the image
to a file.  You can't explicitly tell it to do that.  It's apparently
done every time you hit the "Scan" button at bottom  left.   This  is
just  another  item in the list of bizarre "What were they thinking?"
design features of this perverse app.

(Maybe by the time you read this, someone at Apple will have read  it
and ordered a few UI changes to Scanner. But more likely they'll have
created a new app with a different name, and not told their  previous
customers what it's called.  ;-)