An image processing apparatus provided with a display unit for displaying an operation picture, showing control indicia (e.g., icons) corresponding to multiple image processing functions, is operated to display the operation picture on an external display device. The operator selects one of the indicia shown on the external display device by operating an input device, such as touch screen of the apparatus or a remote control, to indicate the position of the desired one of the indicia. The operator can thereby quickly and reliably select an image processing function to be executed, without any need to view an operation picture on the display unit when making the selection.