A database preparing method prepares a design database from which design database image elements are retrievable to build composite design images for decision making. The entire design image, including a plurality of separable image elements, is input into a processing unit. At least one of the image elements is extracted from the entire design image. The characteristic data which (i) identifies the extracted image element and (ii) corresponds to the entire design image is recorded and stored into a memory. The foregoing steps are repeated to build the design database. In a database retrieving method, a partial image of an entire image is input as a retrieval key. The entire image which corresponds to the retrieval key is retrieved from a database stored in a memory. The retrieved entire image is output.