Urban mobility is an important part of many studies related to the planning of large urban areas. This paper describes an approach for the evaluation of urban mobility as geosocial dynamics on the territory with high population density on the basis of surveillance cameras. We examine various methods of image and video processing for the evaluation of people flow. As a result, we propose a fast processing and low-cost method for general purpose cameras for the estimation of the number of moving people at a particular point in the city. A case study for some locations in St.Petersburg is considered.