Hold on a second.....
It may be a long shot (and I'm certainly no expert on this), but there are maybe a couple of arguments you could use:
Mort, you could argue that you own the copyright in
(1) the way scans are arranged when viewed; and/or
(2) the way the scans have been collected
rather than in the content of the scans themselves.
An example of the first right would be a recently published book with a Shakespear play in it. Although the copyright in the play itself has long since expired, the publisher owns the copyright in the typographical arrangement of the play.
The slight problem with this is that it tends to relate to 'typographical arrangements' rather than arrangements of, say, computer scans.
In relation to the second right, presuambly you've used some sort of database which the user accesses to get to the scans? The creation of this database involved 'labour, talent and judgment' (or something like that) and so could be copyright protected.
Like I said, it's a bit of a long shot, but if you mention these 'other' copyrights that you own (rather than those owned by Newsfield or whoever it is now), it might be enough to make these guys think, "Bollocks, I thought I'd be okay because I was just copying copies".