Encoding signals with printed clear topcoats

An image processing method comprising:

• obtaining first imagery representing a substrate, the substrate comprising a color ink printed thereon and a clear topcoat layer arranged according to a 2D encoded signal, the 2D encoded signal comprising positive signal components, in which the first imagery is associated with a first capture angle between a camera and the substrate;
• analyzing the first imagery to decode the 2D encoded signal;
• inverting the first imagery to yield inverted first imagery and attempting to decode the 2D encoded signal from the inverted first imagery;
• obtaining second imagery representing the substrate, in which the second imagery is associated with a second capture angle between the camera and the substrate, the first capture angle and the second capture angle comprising different capture angles;
• inverting the second imagery to yield inverted second imagery and attempting to decode the 2D encoded signal from the inverted second imagery;
• in which the substrate, or an object associated with the substrate, is deemed authentic when the 2D encoded signal is detected from:
• i) the inverted first imagery or the inverted second imagery, and ii) the first imagery or the second imagery.