1. An input apparatus for use in a portable device, comprising: a camera for capturing an image; a storage unit which stores a key-hand mapping table for mapping segments of a hand to a plurality of keys, respectively, according to predetermined criteria; a display unit which displays, in an input mode, the captured image thereon; and a control unit which activates the camera during the input mode, controls the display unit to display the captured image, assign the plural keys to the segments of the hand based on mapping information of the key-hand mapping table, detect an image change in one of the segments displayed on the display unit, and input the key mapped to the segment at which the image change is detected on the display unit.