An impairment signal is introduced into an original visual signal, either electronically or optically, that is not noticeable in a display of the original visual signal but is noticeable in a copy made of the display by a camcorder or other camera, thereby discouraging the unauthorized recording of such displays. One application is to protect commercial movies against being copied in a theatre by a camcorder and distributed. In one form, the added impairment signal includes alternate transparent and dark regions moving across the screen or other display device. The degree of opacity of the dark regions and their speed of movement across the display are selected to make them unnoticeable in the theatre but highly noticeable in a camcorder copy of the movie that is made at a lower frame rate than that at which the movie is displayed.