Forensic feature for secure documents
A forensic feature for a secure document comprises a base document layer and a covert material applied to the base document layer. The covert material includes a carrier and forensic material within the carrier. The forensic material includes a ratio of salts or oxides of metals, such as rare earth metals. The ratio is selected to correspond with a source of the document. The forensic material may be mixed into a coating or ink that is applied at predetermined locations on a secure document. The ratio is then measurable from metal ion signals of the salts or oxides. This ratio, or some metric derived from it, may be linked with information embedded elsewhere in the document to enable verification of the document. Another forensic document feature has a forensic metric that is measurable from a covert material in the document, and this forensic metric corresponds to a source of the document. A blocking layer applied over the covert material prevents access to the covert material such that at least partial destruction of the document is required to measure the forensic metric. The blocking layer may have a blocking property that blocks electromagnetic waves from activating the covert material, or blocks the electromagnetic waves from the covert material in response to the activating waves. The blocking layer is deconstructed to access the forensic feature, verify the document and perform forensic tracking.
1. A method of making a forensic feature for a document comprising:
providing a base document layer of a document;
applying a covert material to a portion of the base document layer, the covert material including a carrier and a mixture of forensic materials within the carrier, the mixture of forensic materials including a ratio of materials selected from the group comprising a salt and an oxide of metal;
applying a blocking layer over the covert material, the blocking layer obscuring the covert material on the base document layer and preventing access to the covert material without damaging the blocking layer; and
applying a machine readable data carrier to the document, the machine readable carrier storing data indicating at least one forensic metric of the covert material.
2. The method of claim 1 wherein the blocking layer prevents access to the mixture of forensic materials such that at least partial destruction of the blocking layer by tearing or combustion is required to measure the ratio.
3. The method of claim 1 further comprising computing a metric related to the ratio and embedding the metric in a layer in the document.
4. The method of claim 3 further comprising embedding the metric in a layer that includes the covert material.
5. The method of claim 3 further comprising steganographically embedding the metric in the document.
6. The method of claim 3 further comprising embedding a digital watermark carrying the metric in an image on the document.
7. The method of claim 1 wherein the covert material is printed on the base layer.
8. An identification document comprising:
a first document layer;
a covert material applied to a portion of the first document layer, the covert material including a carrier and a mixture of forensic materials within the carrier, the mixture of forensic materials including a ratio of materials selected from the group comprising a salt and an oxide of metal;
a blocking layer applied over the covert material, the blocking layer obscuring the covert material and preventing access to the covert material without damaging the blocking layer; and
a machine readable data carrier applied to the identification document, the machine readable carrier storing data indicating at least one forensic metric of the covert material.
9. The identification document of claim 8 wherein the machine readable data carrier is steganographically embedded in the document.
10. The identification document of claim 9 wherein the machine readable data carrier is a digital watermark embedded in information printed on the document.
11. The identification document of claim 8 wherein the data indicating at least one forensic metric of the covert material includes data indicating a forensic metric mathematically related to the ratio.
12. The identification document of claim 8 wherein the data indicating at least one forensic metric of the covert material includes data identifying a location of the covert materials on the first document layer.
13. The identification document of claim 8 wherein the covert material is the same color as the first document layer such that the covert material is not visible.
14. The identification document of claim 8 wherein the mixture of forensic materials including the salt and the oxide of metal is white in color such that it can be mixed with a colored ink without affecting the color of the ink.
15. The identification document of claim 8 wherein the data indicating at least one forensic metric of the covert material includes a key for decrypting the forensic metric of the covert material.
16. The identification document of claim 8 wherein the covert material comprises a coating.
17. The identification document of claim 8 wherein the covert material is printed on the first document layer.
18. The identification document of claim 8 wherein the ratio is measurable from metal ions of the mixture of forensic materials.
19. The identification document of claim 8 wherein the blocking layer prevents access to the mixture of forensic materials such that at least partial destruction of the blocking layer by combustion is required to measure the ratio.
20. An identification document comprising:
a first document layer;
a covert material applied at a location on the first document layer, the covert material including a carrier and a mixture of forensic materials within the carrier, the mixture of forensic materials including a ratio of materials;
a blocking layer applied over the covert material, the blocking layer obscuring the covert material; and
a machine readable data carrier, different from the covert material, applied to the identification document, the machine readable carrier storing data indicating the location of the covert material on the first document layer.