1. A method, comprising: examining a video signal being generated by a computer system and applied to a display screen to locate image areas in which the video signal changes from frame to frame; converting RGB pixel values in the video signal into luminance values (Y) in order to determine luminance values of Y as R/4+G/2+B/8, where R is a red component, G is a green component, and B is a blue component of the RGB pixel values: defining a bounding box around the image areas to provide an area of interest; and detecting a watermark in said area of interest.