1. A classifying method of classifying an article into one of a plurality of groups based on an evaluation value for an image of the article, the method comprising: a creating step of creating, based on sample images, which are images of a plurality of samples each of which has already been classified into one of the plurality of groups, a list of at least one image feature estimated to have been used to classify each sample; a determining step of determining an evaluation method for obtaining the evaluation value, the evaluation method using a feature amount of the at least one image feature included in the list as a parameter; a first obtaining step of obtaining evaluation values for the sample images by the determined evaluation method; a changing step of changing the evaluation method by changing in the list, so that an evaluation value of at least one sample image having a singular evaluation value among the sample images is changed, and a degree of dissimilarity in an evaluation value range for sample images between the plurality of groups is increased; and a second obtaining step of obtaining the evaluation value for the image of the article based on the changed evaluation method, and classifying the article into one of the plurality of groups based on the obtained evaluation value for the image of the article.