🚀 go-pugleaf

I'm been curious about the following issue for some time now and
haven't gotten a good answer.  There are a number of so called
`Copyright Free' collections of clipart.  Dover publishes quite a
few of them.  They are clearly marked Copyright Free, usually on the
cover.  However, inside there is usually a restriction on the use of
the pictures that goes something like:
	... You may use the designs and illustrations for graphics and
	crafts applications, free and without special permission, provided
	that you include no more than ten in the same publication or 
	project. ...

	Republication or reproduction of any illustration by any other
	graphics service or in any other design resource is strictly
	prohibited.

Now, the illustrations were originally published in late nineteen hundreds
and thus the orriginal copyright has expired.  So my question is: How can they
enforce this?  What is to stop someone from using, say, 11 illustrations in
a single document?  What's to stop some one from republishing the whole book
minus anything that is orriginal with the compiler of the book (ignoring 
the issue of quality reproduction)?  Or for that matter, scanning the images 
in and putting them on a BBS or file server in a company?

The best answer I've heard is that the publisher is copyrighting the 
collection and not the individual items.  This seems a bit farfetched
since it doesn't explain how they can limit the number of images you may
use.  My guess is that they are simply blowing smoke.

This must have been talked through before, anybody got any ideas or info?