1. A method for detecting an object using a perspective plane, comprising: determining a perspective plane for a background scene; determining a first minimum size for detecting an object at a reference position within the perspective plane; determining a second minimum size at a second position within the perspective plane, the second minimum size being based on the first minimum size at the reference position and the relationship between the reference position and the second position with respect to the perspective plane; and detecting a moving object within the background scene based upon the determined perspective plane and the first minimum size and second minimum size.