Precision watermarking of covert and overt authentication features

A method of making a security document, the method comprising:

• forming, in or on a substrate, a first indicia occupying a first predetermined region of the substrate, the first indicia having a first pattern comprising a first reference point and a second reference point;
• and
• forming, in or on the substrate, a second indicia occupying a second predetermined region of the substrate, the second indicia having a second pattern comprising a third reference point,
• wherein the first reference point, second reference point, and third reference point fit a first line,
• wherein a distance between the first line and the first reference point comprises a first perpendicular offset,
• wherein a distance between the first line and the second reference point comprises a second perpendicular offset,
• wherein a distance between the first line and the third reference point comprises a third perpendicular offset, and
• wherein each of the first, second, and third perpendicular offsets are equal to or less than a first threshold value.