It sounds like you are talking about a camera that has the ability to read plates built in. If so, try the free VMS that would be available by the manufacturer and see if it accomplishes what you are looking for.
The methods mentioned above, as well as Plate Recognizer, are a 3rd party and can be accomplished with a camera that does not have the ability to read plates built in.
If you have a camera that has the ability to read plates as part of the system, they you should try to find a solution that will not cost you additional money, or return that camera for a cheaper one and use one of the 3rd party platforms.