A video displaying method. The method includes applying a first frequency modulation in time domain on an original video thereby obtaining a first modulated video; applying a second frequency modulation in spatial domain on the first modulated video thereby obtaining a second modulated video including a first invisible-light image; and displaying the second modulating video with a corresponding frame rate. A time-domain frequency of the first invisible-light image is in a first range unrecognizable by a naked eye and recognizable by a video recorder. A spatial-domain frequency of the first invisible-light image is in a second range unrecognizable by the naked eye and recognizable by a video recorder.