Interesting question, but I suspect that there isn't such a convincing use case for this as forged currency is for tracking color printers. Does government use

Interesting question, but I suspect that there isn't such a convincing use case for this as forged currency is for tracking color printers. Does government use paper as a security boundary, and if that's the issue, wouldn't it suffice to have the scanners in the relevant offices log everything they are scanning (which I think they already do)? Also, almost all such watermarks would be easily destroyed by bitonalization and despeckling, which is usually done anyway to reduce the file size (e.g. it's part of the default operation of https://github.com/4lex4/scantailor-advanced https://github.com/4lex4/scantailor-advanced ). Arguably the same is true for yellow dots if one is leaking scanned printouts, but identifying leakers is not the main purpose of the dots... If one really wanted to, one could try embedding little holes into certain letters and hope they survive the smoothing algorithms and don't stand out too much. Not sure how successful that would be, though.