1. An apparatus for extracting features of predetermined subregions of a skin pattern image, comprising: an image memory for storing image data of the skin pattern image; a filter file for storing a plurality of filters consisting of two-dimensional data prepared according to the features to be extracted; filtering means for outputting filtered data sets, each of said filtered data sets obtained from said image data by convolution calculation with each of said plurality of filters; image intensity calculation means for calculating image intensity of each of the predetermined subregions of each of said filtered data sets; and feature extracting means for determining the features of the predetermined subregions of the skin pattern image referring to said image intensity of each of the predetermined subregions of each of said filtered data sets, wherein: said feature extracting means determines the features of a predetermined subregion of the skin pattern image according to feature parameters minimizing an evaluation function, said evaluation function being a linear function of said image intensity of each of the subregions of one of said filtered data sets corresponding to a feature parameter assigned to said each of the subregions, and a value corresponding said feature parameter assigned to the predetermined subregion compared to the feature parameters assigned to the subregions neighboring the predetermined subregion.