1. An image processing device for comparing comparison feature quantities of a part point of an object on an image between a registered image and an input image, and executing authentication of the object or executing estimate of an attribute or a state of the object, the image processing device comprising: a storage device configured to store program codes; and a processing unit configured to execute the program codes to operate: a part-point specifying unit configured to specify a part point of the object; a feature-quantity extracting unit configured to extract one or a plurality of feature quantities from a pixel of a sampling point or from a pixel group including the pixel of the sampling point, for each of a plurality of sampling points, and extract candidate feature quantities corresponding to the part point constituted by the extracted plurality of feature quantities corresponding to the respective sampling points, the plurality of sampling points comprising the part point specified by the part-point specifying unit and at least one point on the image other than the part point; and a feature-quantity generating unit configured to generate one or a plurality of comparison feature quantities corresponding to the part point based on a predetermined standard by using the candidate feature quantities extracted by the feature-quantity extracting unit; wherein the predetermined standard includes inverted positive and negative values of feature quantities of the candidate feature quantities.