Authentication of Physical and Electronic Media Objects Using Digital Watermarks

• US 20090067671A1
• Filed: 09/09/2008
• Published: 03/12/2009
• Est. Priority Date: 04/17/2000
• Status: Active Grant

• Current Assignee: Digimarc Corporation
• Original Assignee: Digimarc Corporation
• Inventors: Alattar, Adnan M.
• Granted Patent: US 7,822,225 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0028 Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
• CPC Class Codes: H04N 1/32144 embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
• CPC Class Codes: H04N 1/32283 Hashing
• CPC Class Codes: H04N 2201/3205 of identification information, e.g. name or ID code H04N2201/3209 takes precedence
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/3236 Details of authentication information generation
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes

Abstract

Digital watermark methods for encoding auxiliary data into a host signal are used to authenticate physical and electronic objects. One such method computes a content specific message dependent on the host signal, encodes the content specific message into a watermark signal, and embeds the watermark in the host signal such that the watermark signal is substantially imperceptible in the host signal. One specific implementation embeds data representing salient features of the host signal into the watermark. For example, for photo IDs, the method embeds the spatial location of salient features of the photo into the watermark. Another implementation computes a semi-sensitive hash of the host signal, such as a low pass filtering of the signal, and embeds the hash into the watermark. The watermark signal may be content dependent by making the watermark key dependent on some attribute of the signal in which the watermark is embedded. Another approach is to make the watermark key dependent on a user or an attribute of the user. Yet another approach is to use multiple watermark components and multiple watermark detection stages that help identify and screen out invalid watermark signals. Another digital watermarking method for authenticating a media object transforms a media signal to a frequency domain comprising an array of frequency coefficients. It selects a first set of frequency coefficients, and alters the selected first set of frequency coefficients so that values of the coefficients in the set correspond to a pattern. The pattern of the media signal is authenticated by comparing a pattern of the values of the frequency coefficients in the set with an expected pattern.

Claims

1. A method for encoding auxiliary data into a host signal comprising:

providing a plural-symbol watermark message;

computing a content specific watermark key that is dependent on the host signal; and

embedding the watermark message in the host signal such that the watermark signal is substantially imperceptible in the host signal;

wherein the content specific watermark key specifies how or where the watermark message is embedded in the host signal.

2. The method of claim 1 wherein the content specific watermark key represents one or more salient features of the host signal.

3. The method of claim 2 wherein the host signal comprises an image signal, and the salient features include spatial locations of the salient features.

4. The method of claim 3 wherein the image signal comprises a photo of a person, and the salient features include one or more of the following facial features of the person in the photo:

eyes, nose, and mouth.

5. The method of claim 1 wherein the content specific watermark key comprises a semi-sensitive hash of the host signal, where the semi-sensitive hash is defined as a hash that remains substantially unchanged through digital to analog and analog to digital conversion of the host signal.

6. The method of claim 5 wherein the semi-sensitive hash comprises a low pass filtering of the host signal.

7. The method of claim 6 wherein the low pass filtering comprises selecting most significant bits of selected parts of the host signal.

8. The method of claim 5 wherein the host signal comprises a photo of a bearer of a photo identification document that is printed on the document.

9. The method of claim 8 wherein the plural symbol watermark message comprises a unique identifier associated with the bearer, such that the photo identification document is authenticated by scanning the photo, decoding the watermark message to obtain the unique identifier, and comparing the obtained unique identifier with an expected unique identifier for the bearer.

10. The method of claim 9 wherein the expected unique identifier is read from a different part of the photo identification document other than the photo.

11. The method of claim 1 wherein the host signal is an image on an object, and the watermark message comprises a unique identifier associated with a bearer of the object.

12. A computer readable medium on which is stored software for performing the method of claim 1.

13. The method of claim 1 wherein the content specific watermark key specifies how the watermark message is embedded in the host signal.

14. The method of claim 1 wherein the content specific watermark key specifies where the watermark message is embedded in the host signal.

15. A method of encoding a plural symbol auxiliary message into content, comprising:

(a) processing received input content to yield characteristic information related thereto;

(b) defining a watermarking key that includes said characteristic information yielded from the input content;

(c) obtaining a plural symbol watermark message; and

(d) performing an algorithmic transformation on said watermark message, using said watermarking key, to steganographically embed the watermark message into the content, yielding encoded content.

16. The method of claim 15 wherein:

the input content includes a text portion and an image portion;

the characteristic information is derived from the text portion; and

the method includes embedding the watermark message in the image portion.

17. The method of claim 15 wherein:

the input content includes a first portion, and a second portion distinct from said first portion;

the characteristic information is based on the first portion; and

the method includes embedding the watermark message in the second portion.

18. The method of claim 15 wherein said encoded content includes image information, and the method further includes printing said encoded content on a substrate.

19. A printed document produced according to the method of claim 18.

20. In a method of digitally watermarking content, the method including performing an algorithmic transformation on a plural symbol auxiliary message to yield a watermark signal, and altering the content in accordance with said watermark signal, an improvement comprising deriving a watermark key from data representing the content, wherein the algorithmic transformation is dependent on said derived watermark key.