1. A method for characterizing a physical retail space based on automatic measurement of a demographic composition of a plurality of shoppers in the physical retail space, comprising the following steps of: a) dividing said physical retail space into a plurality of sub-regions, the sub-regions comprising at least one of aisles, entry points, exit points, or predefined areas of said physical retail space, b) capturing a plurality of input video images of said plurality of shoppers in said physical retail space and said retail space sub-regions over a specified period of time by a plurality of cameras, c) automatic measuring demographic information of each shopper in said plurality of shoppers in said plurality of input video images using a computer, said demographic information comprising age, gender and ethnicity information, d) determining statistics of said demographic information and measuring said demographic composition of said plurality of shoppers in said physical retail space and said retail space sub-regions, said demographic composition comprising categories defining entity with a group of products, a group of product types, spaces, areas or display of a group of products, and e) characterizing said physical retail space and said retail space sub-regions based on said demographic measuring and said demographic statistics, said physical retail space characterization comprising at least one of the following: a characterization of said demographic composition of shoppers in said physical retail space and retail space sub-regions; or a characterization of said physical retail space or said retail space sub-regions by product match or media match based on said demographic composition; or a characterization of said physical retail space and retail space sub-regions according to a media effectiveness measurement based on said demographic composition measuring; and f) outputting, by a computer, said physical retail space characterization of said physical retail space and retail space sub-regions.