For performing a fingerprint security function in an electronic device having a camera unit, a focus of a lens in the camera unit is adjusted to a first focus level when a control signal set indicates a normal photograph mode. Alternatively, the focus of the lens in the camera unit is adjusted to a second focus level different from the first focus level when the control signal set indicates a fingerprint photograph mode. Thus, existing components of the built-in camera are used to minimize cost and time for production of the electronic device that performs the fingerprint security function.