Abstract: Embedding data to be embedded as a digital watermark is acquired. Packing data is formed in which the embedding data is repeatedly connected three times or more sequentially without interval. Real embedding information is formed such that a redundancy bit with a fixed length that is used for an error correction of an information bit is added immediately after the information bit in which the packing data is subdivided into data each having a fixed length. The real embedding information is embedded into the image data itself. The embedding mechanism for the information is not easily understood, and security level is high.

Abstract: A justification/authentication personal certificate system stores in a remote database a counterpart of an identifier and a digital watermark contained in the personal certificate. The personal certificate includes the digital watermark embedded in an authentic image such as a facial photograph, a retinal scan, or a fingerprint. When the personal certificate is used, the authentic image is read from the personal certificate, and the digital watermark information is extracted. The digital watermark information and the identifier are compared with the counterparts stored in the database. If the extracted digital watermark information is identical to the information in the database, then the personal certificate is judged to be unjustifiable. In one embodiment, at least one of the identifier and digital watermark are changed each time the system justifies the personal certificate.

Abstract: A high-pressure sodium lamp is connected to a d.c. power supply through a ballast, to operate it with a current containing a d.c. component. The relation between the ratio l/d of the inter-electrode distance l (mm) to the inner diameter d (mm) of the arc tube of the high-pressure sodium lamp and the sodium vapor pressure P.sub.Na (kPa) in the arc tube is maintained at P.sub.Na .gtoreq.6.0 (l/d-5.8), thus making it possible to operate the high-pressure sodium lamp with a current containing a d.c. component without causing a significant color separation which otherwise might be the result of cataphoresis.