1. A passenger counting system comprising: a first image capturing device having a lens, the first image capturing device being arranged outside a vehicle for capturing a lateral image of inside of the vehicle from a lateral direction of the vehicle; a second image capturing device having a lens, the second image capturing device being arranged outside the vehicle for capturing a frontal image of inside of the vehicle from a frontal direction of the vehicle; and one or more processors configured to: detect a number of faces from the lateral image; detect a number of faces from the frontal image; and determine a number of persons present in the vehicle based on the number of faces detected from the lateral image and the number of faces detected from the frontal image.