1. A read image capturing system, comprising: a reading device that reads images from original documents; a read-image capturing circuit that captures read images read by the reading device; and a signature managing circuit that manages signature images for causing the read-image capturing circuit to capture, on a per-user basis, read images as for-capture signature images; wherein the read-image capturing circuit in capturing a read image correlates the read image to a user correlated by the signature managing circuit with a for-capture signature image whose degree of resemblance to a signature image included in the read image is at least a for-capture degree of resemblance, the signature managing circuit manages, as capture-prohibiting signature images on a per-user basis, signature images for prohibiting the read image capturing circuit from capturing read images, and the read-image capturing circuit prohibits read-image capture when a degree of resemblance between a signature image included in a read image, and a capture-inhibiting signature image managed by the signature managing circuit is not less than a capture-prohibiting degree of resemblance that is higher than the for-capture degree of resemblance.