An image monitoring system includes a recorder that records an image captured by a camera via a network. The system is controlled to display the present image captured by the camera or a past image recorded on the recorder. A moving object is detected from the image captured by the camera, the detector including a resolution converter for generating an image with a resolution lower than the resolution of the image captured by the camera. A moving object is detected from the image generated by the resolution converter and positional information on the detected moving object is output. The positional information of the detected moving object is merged with the image captured by the camera on the basis of the positional information.