Provided is a device including a display unit configured to display a main window for displaying an image on a screen of the device, and to display, on the main window, a user interface for receiving an input for selecting an area of the image to be displayed on the main window and a first partial image selected via the user interface, a user input unit configured to receive a user input for selecting a point on the user interface; and a controller configured to control, when the user input for selecting the point on the user interface is received, the display unit to display a sub-window on the main window on which the first partial image is displayed, wherein the sub-window displays a second partial image of the image which corresponds to the selected point on the user interface.