1. A method of recording image data, including: attaching an identification tag, to which data relating to a subject to be picked up is recorded, to the subject to be picked up; determining whether or not a time difference between the time at which image data of the subject to be picked up is obtained and the time at which tag data of the identification tag is read is within a preset specified time; associating the image data with tag data under the condition that both the image data obtaining work and the tag data reading work are performed within the specified time; and making a record.