| 摘要 |
A method of protecting a security document from counterfeiting includes applying at least one security element containing a concealed Fourier pattern to the document. The concealed Fourier pattern is produced from a master Fourier profile, and is applied to the document by embossing, engraving, laser ablation or chemical etching, and/or by a cylinder or plate bearing the master Fourier profile. When a counterfeit security document produced without knowledge of the master Fourier profile is scanned or imaged and subjected to a Fourier transform, the resulting test Fourier pattern will differ from a master Fourier pattern corresponding to the master Fourier profile for the authentic security document. In a particular embodiment, the concealed Fourier pattern is applied to the document by rotogravure printing. |
