Those images are at 300dpi, so on a 96dpi monitor you're seeing them roughly three times actual size. The cards I bought are represented by the jack on the right; the jack on the left is from a pack I bought a while back. You can see they're the same pattern, although with some minor differences. The one on the left has better-quality artwork but the one on the right is in better condition and the colours have faded less.
I didn't know who manufactured these cards when I bought the first pack three years ago. Since then, though, I've found out that they were by my favourite manufacturer, Dondorf. I might have known. Dondorf numbered their card decks (not sequentially, apparently) and this is number 1320; the fact it's not 1,320 probably means that the numbers mean something, but I don't know what that is.
The pack dates from 1913, which came as a surprise. Its square edges and lack of indeces ought to make it older than that, but I suppose their very size would force some compromises in their manufacture. There's no tax stamp, which is less of a surprise as the stamp would cover most of the card, if not all of it. The Dondorf marque usually appears somewhere on the Jack of Clubs, but I've been over them with a magnifying glass and it's not there. Maybe you'll have better luck from the scans...
I still have no explanation as to why the red 5s and 6s in the pack I bought first are less heavily used than the other cards in that pack, though.
PS: if you want your own pack of Dondorf 1320, there's an immaculate set for sale on eBay as I write this. Feel free to bid on it, as I've already been outbid on it myself so want to see the person who outbid me punished...