There are many ways to make custom playing cards, here is my first approach, and following instructables like How to make a custom set of playing cards - Approach 2
, I will show some other approaches. I believe this is the best I have tried so far.
Why create a custom set of playing cards? Not because you want "vanity cards", there are web sites that will do that for you (another instructable) but because you want a set of cards you can not get, like for a game you are designing or a commercial game that is out of print.
The example I am using in this instructable are cards from the game I am designing called "I, Detective".