The present invention relates generally to documents, e.g., such as legal tender, currency and identification documents, and apparatus for encoding documents. One claim recites: a physical document including a machine-detectable hidden signal. Presence of the hidden signal is determined by collecting visible light image data associated with the document and transforming the image data to a complementary domain to generate transform data. Presence of a telltale pattern in the transform data indicates a presence of the hidden signal. The hidden signal is associated with a type or status of the physical document. One type is legal tender. Another type is an identification document. An example of status is "do not copy". Of course, other combinations are claimed as well.
RELATED APPLICATION DATA
This application is a continuation of U.S. patent application Ser. No. 11/377,708, filed Mar. 15, 2006, now abandoned, which is a continuation of application Ser. No. 10/656,076 filed Sep. 4, 2003 (now U.S. Pat. No. 7,016,516), which is a continuation of Ser. No. 10/164,899, filed Jun. 4, 2002 (now U.S. Pat. No. 7,043,052) which is a continuation of application Ser. No. 09/198,022, filed Nov. 23, 1998 (now U.S. Pat. No. 6,546,112), which is a continuation of application Ser. No. 08/763,847 (now U.S. Pat. No. 5,841,886), filed Dec. 4, 1996, which is a continuation of application Ser. No. 08/512,993, filed Aug. 9, 1995, now abandoned, which is a continuation-in-part of each of applications Ser. No. 08/436,098 (now U.S. Pat. No. 5,636,292), Ser. No. 08/436,099 (now U.S. Pat. No. 5,710,834), Ser. No. 08/436,102 (now U.S. Pat. 5,748,783), Ser. No. 08/436,134 (now U.S. Pat. No. 5,748,763), and Ser. No. 08/438,159 (now U.S. Pat. No. 5,850,481), each filed May 8, 1995. Application Ser. No. 08/512,993 is also a continuation-in-past of application Ser. No. 08/327,426 (now U.S. Pat. No. 5,768,426), filed Oct. 21, 1994, which is a continuation-in-past of application Ser. No. 08/215,289, filed Mar. 17, 1994, now abandoned, which is a continuation-in-past of application Ser. No. 08/154,866, filed Nov. 18, 1993, now abandoned.
A robust fingerprinting system is disclosed. Such a system can recognize unknown multimedia content (U(t)) by extracting a fingerprint (a series of hash words) from said content, and searching a resembling fingerprint in a database in which fingerprints of a plurality of known contents (K(t)) are stored. In order to more efficiently store the fingerprints in the database and to speed up the search, the hash words (H(n)) of known signals (K(t)) are sub-sampled (13) by a factor M prior to storage in the database (14). The hash words (H(n)) of unknown signals (U(t)) are divided (16) into M interleaved sub-series (H0(n) . . . HM-1(n)). The interleaved sub-series are selectively (17) applied to the database (14) under the control of a computer (15). If only one of the sub-series sufficiently matches a stored fingerprint, the signal is identified.
A security document comprising artwork including a security pattern, characterized in that the security pattern has the form of a line structure in which lines width or line spacing is adjusted to carry predefined data. The artwork is generated by the modifying at least one color of at least a part of the artwork to embed the security pattern in the artwork. Methods for detecting the security pattern include use of a frequency domain structure to detect the security pattern despite rotation and scaling of the document, use of signal tiling to improve signal detection, and use of statistical analyses to verify detection of the security pattern.
Hashes are short summaries or signatures of data files which can be used to identify the file. Hashing multimedia content (audio, video, images) is difficult because the hash of original content and processed (e.g. compressed) content may differ significantly.The disclosed method generates robust hashes for multimedia content, for example, audio clips. The audio clip is divided (12) into successive (preferably overlapping) frames. For each frame, the frequency spectrum is divided (15) into bands. A robust property of each band (e.g. energy) is computed (16) and represented (17) by a respective hash bit. An audio clip is thus represented by a concatenation of binary hash words, one for each frame. To identify a possibly compressed audio signal, a block of hash words derived therefrom is matched by a computer (20) with a large database (21). Such matching strategies are also disclosed. In an advantageous embodiment, the extraction process also provides information (19) as to which of the hash bits are the least reliable. Flipping these bits considerably improves the speed and performance of the matching process.
The present invention provides methods and systems that are helpful for authenticating or protecting physical and electronic documents like financial documents and identification documents. One claim recites a method including: receiving digital data corresponding to a physical document; transforming the digital data into a frequency domain; comparing characteristics associated with the transformed digital data to predetermined characteristics that are associated with a first document type, and if the characteristics coincide, determining that the physical document is of the first document type; and if the characteristics do not coincide, comparing the characteristics of the transformed digital data to predetermined characteristics that are associated with a second document type, and if the characteristics coincide, determining that the physical document is of the second document type. Of course, other claims and combinations are provided as well.
