1. An input apparatus for use in a portable device, comprising: a camera for capturing an image of a hand; 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 configured to: activate the camera during the input mode and control the display unit to display the captured image, display the plurality of keys mapped to the segments of the hand based on the key-hand mapping table, in response to detecting that a shape of the hand satisfies a predetermined condition, output a message requesting a change of the shape of the hand, in response to detecting that the shape of the hand does not satisfy the predetermined condition, in response to detecting an image change in one of the segments displayed on the display unit, input a key of the plurality of keys mapped to the segment where the image change is detected on the display unit, and in response to detecting, via the camera a particular change in the hand folding at least one finger while other fingers are extended, removing the displayed plurality of keys to display a numeric keypad mapped to at least some of the segments of the hand based on the key-hand mapping table. wherein the control unit controls the display unit to display a character input region displaying one or more characters inputted via the mapped plurality of keys, the character input region displayed separately from the mapped plurality of keys.