1. An image feature generating device for generating image feature descriptors for similarity calculation from input image data configured so as to perform a DCT (discrete cosine transform) on the input image data to produce DCT coefficients thereon, and perform coefficient transform on the produced DCT coefficients in a manner that fine quantization is carried out on a range of a portion of each of the produced DCT coefficients having a small amplitude and coarse quantization is carried out on a range of a portion of each of the produced DCT coefficients having a large amplitude, in order to generate the image feature descriptors, using the transformed and quantized DCT coefficients as the image feature descriptors.