1. An image processing sensor for performing predetermined image processing on an image of an inspection target object to detect that the inspection target object is a non-defective product or a defective product, the image processing sensor comprising: an imaging unit configured to image the inspection target object; a display unit configured to display a live image of the inspection target object acquired by the imaging unit; an operation unit configured to receive an instruction for storing as a still image in a memory the live image displayed by the display unit so as to register the live image; a threshold calculating unit configured to calculate a threshold with respect to a matching degree indicating a degree of feature matching of a first image that includes the inspection target object that represents the non-defective product and a second image that represents an image other than the non-defective product, the first image and the second image being registered according to the instruction received by the operation unit; and a display control unit configured to cause the display unit to display the first image and the second image as the still image used for the calculation of the threshold by the threshold calculating unit, wherein the display control unit causes the display unit to display, on a first registration screen for registering the live image corresponding to one image of the first image and the second image, the live image acquired by the imaging unit and, after receiving, with the operation unit, an instruction for registering the live image corresponding to the one image in a state in which the live image corresponding to the one image is displayed on the first registration screen, the display control unit causes the display unit to display, on a second registration screen for registering the live image corresponding to the other image of the first image and the second image, the live image acquired by the imaging unit and the already registered one image as the still image.