1. A method of generating feature information using 2nd-order independent component analysis (ICA), the method comprising; (a) performing PCA on an input original image and generating a low-pass filtered image by removing high-frequency component from the original image; (b) subtracting the low-pass filtered image from the original image and obtaining residual image having only frequency-components; and (c) performing ICA on the residual image and generating feature information corresponding to the original image.