Bus Passenger Counting System

I want a passenger counting system for my public bus .The software should count all the passenger climbing on my bus throughout the day and give a reading at the end of the day.IT MUST COUNT EVERY PASSENGER ONLY ONCE(it is very important).I have a wifi cctv camera installed on the bus overlooking the only entrance .Line based counting would not work as the helper often stands at the entrance. OPTIONAL:I want to make the software subscription based ,making my pc as a server.