Provided is a monitoring system, comprising a imaging-side device, and a matching-side device which receives image data from the imaging-side device and matches the image data. The imaging-side device wirelessly transmits, to the matching-side device, feature value data which denotes feature of an image subject. Upon receiving the feature value data, and on the basis of the result of a comparison between the feature value data and feature value reference data, the matching-side device wirelessly transmits image data request information to the imaging-side device. Upon receiving the image data request information, the imaging-side device wirelessly transmits image data to the matching-side device.