1. An image searching method, comprising: (a) obtaining, by an image search apparatus, feature descriptors of an input image; (b) obtaining, by the image search apparatus, words to which the respective features correspond, and adjacent words that are adjacent to the respective words to which the features correspond, wherein when a first word cell of a plurality of word cells that are included in a visual feature space is assigned to a word, an adjacent word is a word assigned to at least one second word cell of the plurality of word cells, the second word cell being adjacent to the first word cell to which the word is assigned, wherein the plurality of word cells is assigned to different words, and at least one word being within a predetermined distance from the word is designated as the adjacent word, wherein the plurality of word cells in the visual feature space is formed by obtaining features of a plurality of respective images stored in the database, and clustering the features of the plurality of images based on the locations in the visual feature space, and the plurality of word cells is assigned to different words, and further wherein at least one of the words is obtained by using information on center points, each of which is a mean value of features of images that correspond to the respective word cell, to compare distances between the respective features of the input image and the respective center points of the plurality of word cells, and obtaining, for the word, a word assigned to a word cell of which center point is most closely adjacent to the corresponding feature of the input image; (c) searching for, by the image search apparatus, an image that is identical or similar to the input image based on information associated with a first group of images corresponding to the word and information associated with a second group of images corresponding to the adjacent word, the information on the first and second groups of images being stored in a database, wherein the information on the first group of images corresponding to the word includes identification symbols and feature descriptors of the respective first group of images corresponding to the first word cell to which the word is assigned from among the plurality of word cells in the visual feature space, and the information on the second group of images corresponding to the adjacent word includes identification symbols and feature descriptors of the respective second group of images corresponding to at least one second word cell adjacent to the first word cell to which the word is assigned from among the plurality of word cells in the visual feature space.