A method for releasing of a lock function of a terminal including a display unit for displaying an operation state of the terminal and a shoot unit for receiving an image comprising a human face, the method comprising: receiving an input for commanding a lock function setting of the operational state of the terminal, the lock function setting comprising: receiving a first image of a human face by setting a first brightness as brightness of the display unit; receiving a second image of a human face by setting second brightness as the brightness of the display unit, wherein the second brightness is different to the first brightness; and comparing the first and second images to extract an interest region having a brightness difference greater than a first threshold; receiving an input for commanding a lock function releasing on the displayed operation state of the terminal; receiving a third image of a human face by setting a third brightness as brightness of the display unit, wherein the third brightness is the same as the first brightness; receiving a fourth image of a human face by setting fourth brightness as the brightness of the display unit, wherein the fourth brightness is different to the third brightness and the same as the second brightness; comparing the fourth image with the third image within a region corresponding to the extracted interest region of the compared first and second images, and recognizing that the human face acquired after the lock function releasing command is the same as the human face acquired after the lock function setting command, when the brightness change of the corresponding region of the third image and the fourth image is equal to or greater than a second predetermined threshold, wherein the second predetermined threshold is smaller than the first threshold. receiving an input for commanding a lock function setting of the operational state of the terminal, the lock function setting comprising: receiving a first image of a human face by setting a first brightness as brightness of the display unit; receiving a second image of a human face by setting second brightness as the brightness of the display unit, wherein the second brightness is different to the first brightness; and comparing the first and second images to extract an interest region having a brightness difference greater than a first threshold; receiving a first image of a human face by setting a first brightness as brightness of the display unit; receiving a second image of a human face by setting second brightness as the brightness of the display unit, wherein the second brightness is different to the first brightness; and comparing the first and second images to extract an interest region having a brightness difference greater than a first threshold; receiving an input for commanding a lock function releasing on the displayed operation state of the terminal; receiving a third image of a human face by setting a third brightness as brightness of the display unit, wherein the third brightness is the same as the first brightness; receiving a fourth image of a human face by setting fourth brightness as the brightness of the display unit, wherein the fourth brightness is different to the third brightness and the same as the second brightness; comparing the fourth image with the third image within a region corresponding to the extracted interest region of the compared first and second images, and recognizing that the human face acquired after the lock function releasing command is the same as the human face acquired after the lock function setting command, when the brightness change of the corresponding region of the third image and the fourth image is equal to or greater than a second predetermined threshold, wherein the second predetermined threshold is smaller than the first threshold.