| 摘要 |
Security documents (e.g. passports, currency, event tickets, and the like) a re encoded to convey machine-readable multi-bit binary information (e.g. digita l watermark), usually in a manner not alerting human viewers that such information is present. The documents can be provided with overt or sublimin al calibration patterns. When a document incorporating such a pattern is scanne d (e.g. by a photocopier), the pattern facilitates detection of the encoded information notwithstanding possible scaling or rotation of the scan data. T he calibration pattern can serve as a carrier for the watermark information, or the watermark can be encoded independently. In one embodiment, the watermark and the calibration pattern are formed on the document by an intaglio proces s, with or without ink. A photocopier responsive to such markings can take predetermined action if reproduction of a security document is attempted. A passport processing station responsive to such markings can use the decoded binary data to access a database having information concerning the passport holder. Some such apparatuses detect both the watermark data and the presenc e of a visible structure characteristic of a security document (e.g., a printe d seal of the document's issuer). |
