Finding good free licenses plate recognition (LPR) Software is not as simple as it sounds.
Here is a good example of how the Victoria Police went ahead and made their own ALPR system with a few lines of code.
Source: freecodecamp
Free is never truly free it will take time to code and also maintenance after the code is done.
This all goes back to what you need your License plate recognition software for. Besides the coding, you would want to take the security into account since you are dealing with lots of sensitive data that you will need to store somehow.