Duplication-proof paper using spaced apart line sets with horizonal and expanded line portions

A duplication-proof paper, comprising;

• a paper proper comprising an external surface;
• and
• a plurality of line sets arranged and displayed on the external surface, the line sets being spaced apart by a first preset distance, and the line sets each comprising:
• an upper line having a first preset width and comprising at least a first horizontal line portion and at least an upward expanded line portion extending upward and outward from the at least a first horizontal line portion;
• and
• a lower line having a second preset width and comprising at least a second horizontal line portion and at least a downward expanded line portion extending downward and outward from the at least a second horizontal line portion, the at least a second horizontal line portion corresponding in position to the at least a first horizontal line portion, and the at least a downward expanded line portion corresponding in position to the at least an upward expanded line portion, wherein the at least a first horizontal line portion and the at least a second horizontal line portion are spaced apart by a second preset distance,
• wherein the at least an upward expanded line portion and the at least a downward expanded line portion have an expansion zone defined therebetween and are spaced apart by a third preset distance,
• wherein the expansion zones of the plurality of line sets are arranged to form a pattern, and
• wherein the first preset distance ranges from 0.01 mm to 0.6 mm, the second preset distance ranges from 0.01 mm to 0.15 mm, the third preset distance ranges from 0.01 mm to 0.45 mm, the first preset width ranges from 0.005 mm to 0.05 mm, and the second preset width ranges from 0.005 mm to 0.05 mm.