In an image communication system including a server which stores image data encoded in accordance with a hierarchy coding, and a client configured to download the image data from the server and display the image data, the server determines on the basis of a request received from the client whether a specific command is requested, when the specific command is requested, generates return data by adding additional data representing the encoding condition of the image data encoded in accordance with the hierarchy coding to image data which has undergone processing designated by the specific command, and transmits the return data to the client. With this arrangement, the client can receive desired image data by one communication between the server and the client.