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 an image of the inspection target object acquired by the imaging unit; an operation unit configured to receive an instruction for registering the image displayed by the display unit; 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 including the inspection target object that should be distinguished as the non-defective product and a second image not including the inspection target object that should be distinguished as 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 images 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 one image of the first image and the second image, as a live image, the one image acquired by the imaging unit and, after receiving, with the operation unit, an instruction for registering the one image, causes the display unit to display, on a second registration screen for registering the other image, as the live image, the other image acquired by the imaging unit and, as a still image, the already registered one image.