In a conventional client/server type image database for centralized management of image data, upon transmission of image as a search result from a server to a client, since it takes time for the client to display the image due to a network band, the image search cannot be always performed efficiently. Accordingly, in a client process, a feature amount is extracted from a search image, and the extracted feature amount is transmitted to a server process. Then, the result of search by the server process based on the feature amount and a GUID specifying the image database are received from the server process, and image data which is not cached in the client, is requested from the server process based on the search result and the GUID.