My friend also did something similar. He created license plate recognition. The software looks for motion, then looks for shapes that resembles license plates. After that, the software adjusts the plate image to correct for off angle image. Next he uses character recognition software to read the plate. The software finally draws a box around the plate and writes the plate number on the image of the vehicle.

My friend took it a step further and set his raspberry pi to text every time it detected a plate with the image of the vehicle and the plate number. 

He had to shut the texting down because he was getting too many texts even though he lived on a cul de sac.