When it comes to reading plates you need:
At least 7 pixels per inch at the target distance. (that is rez AND lens view angle)In my post Doing the math on pixels per inch at a distance for your cam I pointed out the math involved in getting the min number of pixels to be able to make out a plate.
The camera focused for that distanceMost cams are fixed focus and have the lens glued in place so you can not adjust it much less swap it out. To give you and idea watch this video of a guy that swapping out the lens in a Wyze cam. Sadly higher priced brands do similar. You might want to look at my compare between static and auto focus versions of a some Reolink cams.
Enough contrast to make those pixels usable.See this post on low light which helps get you a bit more.
And if the target is moving, a high enough frame rate and shutter speed to minimize motion blur and get a frame in the target range.There is some good info here about frame rates and such needed.
And if you are looking to read them at night you need to think about reflections.Nelly's Security has a nice post about this.
It should be obvious but no tracking or battery powered cams.But if you need convincing read this.
Then there are plugin optionsLike this one for Blue Iris that is on my eval to-do list.
OpenALPR which has and open API and cloud based services.
This post shows how to link Blue Iris and SmartThings through a learning AI system for alerts.