By messing with my screen settings I was able to get cards of about 749 x 1260 pixels (per card - the png images I got were bigger). That is *almost* the image size required by a POD tarot card service.
I've just implemented a universal method for converting my graphics to SVG (for Perilous Shores) so I might as well try it out on this. If everything will be OK, there will be SVG export in Procgen Tarot within a week.