Private and Passenger license plates don't really have so many differences. Both can be obtained as a license plate by anybody and they both have the same design. The main difference between the two is the registration that appears on the plate itself. A private license plate will have a normal, randomly generated registration. A passenger license plate's registration will always be less than six characers.
The Bicentennial license plate commemorated the bicentennial of the Declaration of Independance being signed. It first became an issued license plate in 1971 intending to be issued through 1976. The license plate had two different looks between the two years. From 1971 until 1973 in was a dark blue background with yellow lettering and design. Starting in 1973 and going until 1976 the plate had a lighter blue background with the same yellow lettering and design. Other things to be mentioned about this Bicentennial plate are the second ever use of the letters T and W, in 1971 it was awarded plate of the year by AlPCA (Automobile License Plate Collectors Association), and Pennsylvania was the first state to celebrate the Bicentennial with a license plate.
These are the license plates that can be obtained by any person for their car. They are the plates that are most commonly seen on cars. The design varied throughout the years as new plates were issued.