1. An inspecting device comprising: a read image acquirer configured to acquire a first read image that is obtained by reading a printed matter; a reference image generator configured to generate a reference image based on a source image from which the printed matter has been generated; an inspector configured to inspect the printed matter based on threshold information containing one or more types of thresholds and based on a difference image indicating a difference between the first read image and the reference image; an identifier configured to identify, on the printed matter, an area having a discrepancy between an inspection result and a result of visual check by a user; and a changer configured to change the threshold information to resolve the discrepancy in the area, wherein the read image acquirer further acquires a second read image that is obtained by reading the printed matter on which the area is specified, the identifier identifies the area based on the second read image, the area is specified by a symbol assigned to the printed matter, and the identifier detects the symbol on the second read image and identifies the area based on the symbol.