An alpha channel is added in addition to multiple channels forming an image of an item. A second pixel value differing from a first pixel value, which is assigned to a defect-free region, is assigned to a region corresponding to a defect region in the alpha channel. The image including the alpha channel is divided into multiple image segments. A defect label is assigned to the image segment in which the second pixel value is included in the alpha channel, and a non-defect label is assigned to the image segment, in which the second pixel value is not included in the alpha channel. The alpha channel is removed from the image segments to generate labeled image segment data.