A device includes a display monitor configured to display on a screen of the display monitor at least one of a current image and a preceding image taken by an optical unit, a storage unit configured to store the preceding image, and a control unit configured to display a part of the preceding image on the screen when the current image is displayed on the screen, the displayed part of the preceding image indicating a positional relationship between the current image and the preceding image. The current image is taken when the displayed part of the preceding image substantially overlaps a corresponding portion of the current image such that the current image and the preceding image can be processed to form a panoramic image.