1. A method of determining parking lot occupancy from digital images, the method comprising: obtaining a layout of a parking lot having a plurality of parking spaces; estimating a volume of a parking space for at least one viewing angle of the parking space and the probability that an observed pixel belongs to the parking space volume; acquiring one or more image frames of the parking lot from at east one digital camera; performing pixel classification using at least one vehicle detector on the acquired one or more image frames to determine a likelihood that a pixel corresponds to a vehicle; computing a probability that a parking space is occupied by a vehicle based on a spatially varying membership probability density function and a likelihood of vehicle pixels within a region of interest; and determining parking lot vacancy via a comparison of the computed probability that a parking space is occupied by a vehicle to a pre-determined threshold.