Device and method for controlling a luminance of a flat display minimizes a chip area, and controls a luminance of a desired portion of a display efficiently without an additional power consumption. The frequency locked loop performs a clock multiplication function such that an inexpensive and low frequency external crystal is usable to both clock a processor of the microcontroller with a higher frequency and low-jitter clock signal and to clock a real time clock of the microcontroller with a low frequency time base that is a power of two multiple of one hertz. Processed image data are generated by performing at least one of baseline image subtraction or image suppression on the image data, and a location of at least one possible defect in the structure is identified based on the processed image data. The server transmits the authentication data to the first wireless device so that the first wireless device authenticates the second wireless device using the authentication data upon receipt of a further authentication request from the second wireless device.