1. An image processing device connectable to a check processing device configured to process a check printed by ink including a UV ink readable by an image sensor and a magnetic ink readable by a magnetic sensor, the image processing device comprising: a computer which runs a program configured to acquire a first image from the check processing device that includes a first reflection of a first portion printed by the magnetic ink on a surface of the check exposed to a visible first light, and acquire a second image from the check processing device that includes a second reflection of the first portion printed by the magnetic ink, and fluorescence of a second portion printed by the UV ink on a surface of the check exposed to an ultraviolet second light; apply an edge-extracting image processing filter to the first image and generate a first edge image, and apply the image processing filter to the second image and generate a second edge image; detect common edge parts where a first edge extracted in the first edge image and a second edge extracted in the second edge image are at corresponding positions, removes the common edge parts from the second edge image, and generates a common-edge-removed second image; and show the common-edge-removed second image on a display and execute a payment process based on magnetic information acquired from the check processing device, and wherein the computer is configured to detect the common edge parts based on first vector information of the first edge and second vector information of the second edge, the first vector information comprising a first edge strength and a first direction of the first edge and the second vector information comprising a second edge strength and a second direction of the second edge, wherein the extracted edges of the second portion printed by the UV ink remain in the common-edge removed second image.