Well, modern printers print with 100s of ppi, which on doing some maths suggest around 100 dot in a box of side 1 mm(in 250 ppi, most printers print with more p

Well, modern printers print with 100s of ppi, which on doing some maths suggest around 100 dot in a box of side 1 mm(in 250 ppi, most printers print with more ppi), enough for displaying 64 bit number with hash, even if it only works in binary mode. If more that just on/off can be detected, it can store much more.