If you're able to get images of all of the cards that you want to use, then it's just a matter of creating an asset pack and placing the images inside! The hard part would probably be downloading images of the cards, although this could potentially be made easier by using an online database of cards?
ok, so the only way to add cards to the game and get it to recognize them is by adding them directly into the TabletopClub/cards directory where the original assets are being kept. I've tried adding the custom asset pack into various areas to no avail. It does not recognize any directories outside of the TabletopClub main directories, I followed the tutorial to the letter. Also if you do get this bug fixed, it would be much easier for a user, to click an executable and have a bunch of images in a directory made into a 'stack/deck'.
This is for the windows 64 bit version.
Thank you for letting me know about this!
If you go into the options menu in game, under "General" there is a button to open the "main" assets folder under your Documents (Documents\TabletopClub\assets), it should automatically open file explorer when you click it - try placing your asset pack folder in there and either clicking the "Reimport Assets" button or restarting the game.
If that doesn't get your cards to appear, then it would be much appreciated if you submit a bug report on GitHub so I can try to help you further and track the bug for future reference :)