The projected pattern pitch was 2 min in the angle of view and this was over the resolving power of the human-visual system. The reasons that the projected watermarking patterns were invisible, even though their pattern pitches were over the resolving power of the human-visual system, were considered to be as follows. First, the contrast in the original patterns was low, i.e., it was 30% even when HC was 60. Second, as mentioned before, part of the light did not reflect from the surface of the skin but it was reflected in the skin, and this decreases the contrast of the projected pattern on the human face. As a result, it became less visible.