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 parking space volume for at least one viewing angle of at least one 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 least 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 the at least one parking space is occupied by a vehicle based on a weighted sum of the probability of vehicle pixels within the region of interest of each parking space, wherein the region of interest refers to pixels that can potentially belong to a vehicle parked in a given parking space, wherein the weighted sum comprises a weighting function which gives larger weight to pixels located towards a center of the region of interest of each parking space, the weighting function decreasing the weight of a particular pixel as a distance of the particular pixel to the center increases; and determining parking lot vacancy via a comparison of the computed probability that the at least one parking space is occupied by a vehicle to a pre-determined threshold.