1. A method of inspecting a flat panel display, the method comprising: inputting an image data signal to the flat panel display; obtaining an image displayed on the flat panel display corresponding to the input image data signal with a camera; extracting raw brightness information corresponding to each location from the obtained image; calculating fitting brightness information corresponding to the each location through a curve fitting based on the raw brightness information; calculating a brightness difference corresponding to the each location between the raw brightness information and the fitting brightness information; and detecting stain locations with the brightness difference beyond a predetermined permitted limit, wherein the fitting brightness information corresponds to approximate value of the raw brightness information corresponding to the each location.