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An image formed by the lines printed by intaglio perpendicularly to the lines of the background. When the banknote is viewed at an acute angle, the image becomes visible on the background. It becomes either light on a dark background or dark on a light background. The lines parallel to the direction of eyes look light, and the perpendicular lines look dark. Therefore, the tone of the background and the image change, when the bill is rotated without changing the angle of view (fig. 1).