Digital watermarking systems

1. A method of verifying data comprising;

digitally capturing an image;

computing a first hash of the captured image;

comparing the first hash with a database of hashes, the database of hashes comprising hashes corresponding to previously captured images; and

identifying an attack when the first hash matches at least one hash in the database.

2. The method of claim 1 , further comprising:

enabling further processing when the first hash fails to match any of the hashes in the database.

3. A method of verifying data comprising:

digitally capturing an image;

computing a first hash of the captured image; comparing the first hash with a database of hashes, the database of hashes comprising hashes corresponding to previously captured images, wherein the captured image comprises an embedded watermark,

extracting data from the watermark;

encrypting a request, the request comprising the extracted data and the first hash; and

sending the encrypted request to an external computer, wherein said comparing is performed at said external computer.

4. A method of verifying data comprising:

digitally capturing an image;

computing a first hash of the captured image;

comparing the first hash with a database of hashes, the database of hashes comprising hashes corresponding to previously captured images, wherein the captured image comprises an embedded plural-bit watermark,

extracting plural-bit date from the watermark;

encrypting a request comprising a block of image data from the image;

sending the encrypted request to an external computer; wherein said computing and said comparing are performed at the external computer.

5. A system for exchanging data comprising:

a user terminal comprising a watermark reader, and a capturing device to capture an image of a watermarked document; and

a central site comprising a database of image hashes, wherein said user terminal communicates with said central site, and wherein said reader reads a watermark and computes a hash of a captured image and passes the hash to said central site for comparison with said database of image hashes.

6. A method of preventing online attacks, comprising:

capturing an encoded image;

extracting data from the encoded image;

computing a hash of the captured image;

comparing the hash against previously determined hashes; and

linking the extracted data to other data when the hash does not match any of the previously determined hashes.

7. A method of preventing online attacks, comprising:

capturing an encoded image;

extracting data from the encoded image;

computing a hash of the captured image;

comparing the hash against previously determined hashes; and

disregarding the extracted data when the hash matches at least one of the previously determined hashes.

8. A method comprising:

maintaining a database including a plurality of hashes stored therein;

receiving through a network a first hash derived from image data, the first hash being derived remotely relative to performance of said method;

determining whether the first hash has been previously received with reference to at least the plurality of hashes stored in the database;

disregarding a request associated with the first hash if the first hash has been previously received.

9. A method comprising:

maintaining a database including a plurality of hashes stored therein;

receiving through a network a request and a first hash derived from image data, the first hash being derived remotely relative to performance of said method;

determining whether the first hash has been previously received with reference to at least the plurality of hashes stored in the database;

as a condition of executing the request, requesting validation information from a user associated with the request when the first hash has been previously received; and

executing the request when at least one of the following is met: i) the first hash has not been previously received; and ii) proper validation information is received from a user.