how easy is it to resize the cards this way?
Richmond may be able to tell us whether/how this can be done. But as a practical matter, at least in this case I'd question whether it's worth doing. In the plate image that Zax provided as a .png, each card is 69x97 pixels, so when scaled to 200% these already look rather nasty (pixelated).
While learning to employ SVGs in LiveCode not long ago, I ran across a LC project posted by Paul McClernan on GitHub in which a demo stack displays in sequence the entire deck of 52 playing cards rendered as SVGs. (These whiz by at 1 millisecond per card, but if you slow this down to 500 milliseconds per card, you can see that the images are very impressive and resize flawlessly.) The main point of the demo is to illustrate the utility stack he created, which (in his words) "converts multiple SVG files into a script only library stack that loads an Array of pre-compiled binary SVG Data [that can] provide very fast rendering of many SVG graphics."
https://github.com/PaulMcClernan/OpenXT ... ayLibMaker
Depending upon what Zax has in mind for his project, SVGs might be a better choice for images that need to be resized, whether he employs Paul's strategy or just imports the SVGs into his project using "Import As Control".
(BTW, Paul informed me that although he'd found the playing-card images on the net, he had to convert the text -- i.e., the 1-10 and JQKA in the images -- to outlines because LC SVG doesn't yet support text.)