1. A read image capturing system, comprising: a reading device that reads an image from an original document; a read image capturing circuit that captures the read image read by the reading device; and a signature managing circuit that manages a signature image for causing the read image capturing circuit to capture the read image as a signature capturing image for each user; wherein the read image capturing circuit captures the read image in association with a user who is associated with the signature capturing image by the signature managing circuit, the signature capturing image having a similarity degree with the signature image included in the read image equal to or more than a similarity degree for capture.