1. A method comprising: identifying a watermark image to apply to a video frame, the video frame including a plurality of image pixel data values, each of the image pixel data values designating a color of a corresponding pixel in the video frame, the watermark image including a plurality of watermark pixel data values, each of the watermark pixel data values designating a color change to a corresponding pixel, the watermark image identifying a recipient of the video frame; transforming the video frame from the spatial domain into the frequency domain; superimposing the watermark image on at least a portion of the video frame in the frequency domain to create a watermarked video frame, the watermarked video frame including a plurality of watermarked image pixel data values corresponding to the image pixel data values altered by the color change designated in the corresponding watermark pixel data values; and transmitting the watermarked image to a plurality of video frame recipients, wherein watermarked images transmitted to different recipients include different watermarks; wherein the watermark image comprises an image gradient that represents a gradual, directional change in the color or intensity of the watermark.