Described is a multiple-camera system for use in capturing images of users within a materials handling facility and processing those images to monitor the movement of users. For large materials handling facilities, a large number of cameras may be required to monitor the facility. Processing of the data generated from a large number of cameras becomes difficult. The implementations described herein include a hierarchy that allows image data from any number of cameras within a materials handling facility to be processed without substantially increasing the processing time needed or sacrificing processing capabilities.