How can I set the camera to capture license plate from the real car?
Start putting real cars in front of the camera instead of printed paper? /s
This is a technology that relies on visual references from a single camera image sensor that "sees" the world in two dimensions. It's not like your cell phone that requires several sensors (some very specialized too) to properly detect if a face is real or not. If something looks like a car or a plate, it is going to be recognized as a car or a plate - regardless if it is "real" or "paper". Why are there lots of paper cars in front of your camera anyway? If it's a billboard or something like that, I'm sure you can tell the system to ignore that particular plate number. If there are different fake cars passing by your camera, I really want to know the background/situation!
Odds are you are simply overthinking this "problem" and in real life usage it isn't going to be an issue. If you expect to build a system that is going to be 100% reliable in capturing all the valid plates, while also having zero false triggers, you are going to be in for a rude awakening. There simply is ZERO chance of building such a system with today's technology.