1. An object monitoring system comprising: a memory storing instructions; and at least one processor configured to process the instructions to: create a state image by capturing a state occurring in a first range, create a monitoring target image by capturing a monitoring target present in a second range, detect a specific state from the state image, extract, from the monitoring target image created after the specific state has been detected, a feature used for specifying the monitoring target, based on the status of the monitoring target, and specify, for each type of specific state, as an object, a monitoring target which appears with a high frequency in a plurality of monitoring target images.