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, wherein, the first feature extraction method is different from the second feature extraction method, and the using the second feature extraction method is longer than the using the first feature extraction method.