Dover publishes a lot of odd stuff, what they do varies a lot. They're big in crafts books and historical clip art among other things. They've reprinted some craft books that are a bit important historically.
The cards were published as a book of reprints. Intended as a fun, semi educational thing. There were a few different books
http://books.google.com/books/about/...d=_TZzxR2W-4YC
They also did a book of stickers.
http://www.etsy.com/listing/12623027...ars?ref=market
Steve B