1. An apparatus for identifying an image represented by digital image data, comprising: means for extracting feature data from the digital image data representing predetermined color features of the whole image to be identified; first means for storing a plurality of categories corresponding to color features; second means for storing a plurality of target image data grouped based on the color features of the categories respectively; means for selecting one of the categories corresponding to a color feature of the digital image data from the first storing means; means for comparing the digital image data with the plurality of target image data grouped by the category selected by the selecting means; means for determining a most similar target image data in the plurality of image data in the second storing means grouped by the selected categories based on a comparison result by the comparing means; and means for determining a similarity between the digital image data and the target image data in the second storing means grouped by the selected category by the selecting means.