1. A method of detecting an object, the method comprising: receiving an image; generating first images for performing a first classification operation based on the received image; reviewing first-image features of the first images using a first feature extraction method; first classifying at least some of the first images as second images, the classified first images having first-image features matching first-type features calculated by using the first feature extraction method; reviewing second-image features of the second images using a second feature extraction method; second classifying at least some of the second images as third images, the classified second images having second-image features matching second-type features calculated by using the second feature extraction method; and detecting an object in the received image based on results of the first and second classifying.