Abstract: A communication system includes a community management server used by a communication manager and a participant's terminal used by a community participant participating in communication. The community management server manages multimedia data that has data about the community participant embedded therein, an element symbolizing the community participant, a data content display control part and a participant personal identification authentication part. The participant's terminal includes generation part for generating card-like information as a communication unit. When a plurality of community participants executes communication by using the cards to which the multimedia data are put, they can execute information display of personal information of the community participants, authentication of personal identification, and retrieval/edition of a speech content by using information embedded in the multimedia data.

Abstract: A mark management server for certifying digital data based on a digital mark to enable realization of identity authentication and data certification when the digital data is transmitted or received on a network.

Abstract: Multimedia data having, embedded therein by using electronic watermark technique, data that includes first information to be disclosed, and second information for controlling the data to be disclosed is received by a data terminal via a communication network. The data terminal compares the second information included in the received multimedia data with the condition on the data terminal side. At least part of the multimedia data or first information is not displayed or is made illegible on the data terminal according to a result of the comparison of the second information. The multimedia data or the first information is displayed on the data terminal according to another result of the comparison of the second information.

Abstract: A communication system includes a communication management server used by a communication manager and a participant's terminal used by a community participant participating in communication. The community management server manages multimedia data that has data about the community participant embedded therein, an element symbolizing the community participant, a data content display control part and a participant personal identification authentication part. The participant's terminal includes generation part for generating card-like information as a communication unit. When a plurality of community participants executes communication by using the cards to which the multimedia data are put, they can execute information display of personal information of the community participants, authentication of personal identification, and retrieval/edition of a speech content by using information embedded in the multimedia data.