1. A method of searching for an image similar to a newly taken image from among medical images based on past cases, comprising: calculating, using a computer system, wavelet features of a plurality of images that have been taken and stored in the past; extracting, using the computer system, a keyword included in radiographic interpretation information for each stored image; storing, using the computer system, the calculated wavelet features and the extracted keywords in association with the respective stored images; acquiring, using the computer system, a newly taken image; calculating, using the computer system, a wavelet feature of the acquired image; extracting, using the computer system, a keyword included in radiographic interpretation information corresponding to the acquired image and, on the basis of the extracted keyword, searching for similar radiographic interpretation information from the stored keywords; calculating, using the computer system, a wavelet feature-based spatial distance between the acquired image and each of images corresponding to the radiographic interpretation information found; and outputting, using the computer system, as a search result, any images for which the calculated wavelet feature-based spatial distance is shorter than a predetermined value, in ascending order of the calculated wavelet feature-based spatial distance.