1. An information processing device for inspecting a target image that contains an image of an inspection target, the information processing device comprising: circuitry including at least a processor and a memory, the circuitry configured to: perform pre-processing for comparing the target image with a reference image or a plurality of reference images; define, in the target image, a region of interest (ROI) and surrounding regions that are adjacent to the ROI, and calculate a feature value of the ROI; calculate an outlier from comparison with feature values of images corresponding to the ROI and the surrounding regions in the reference images, the outlier numerically indicating singularity of an image at the ROI; provide, based on the outlier, an indicator to be used for the inspection; and determine defections in the inspection target from the target image by using the indicator.