VEIL modulation is a method of "subliminal" encoding of data in a video image that is similar to a watermark. The encoding consists of alternately proportionately raised and lowered luminance on selected horizontal scan lines. The encoding can be detected using a notch filter centered at half the line frequency. The encoding is lost, however, if the resolution of the video signal is changed downward. The invention preserves the encoding by coding alternate groups of lines, not alternate lines. This allows detection with a notch filter even after a reduction in resolution.