| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem of a conventional electronic mail system that cannot have easily distinguished a received electronic mail, which is really sent from a sender, from a received electronic mail, which is sent form an illegal party pretending to be the sender. SOLUTION: A transmission section generates feature information of an electronic mail main text, generates an authentication image to which authentication information of a sender including the feature information is imbedded as an electronic watermark and transmits the authentication image, and a reception terminal extracts the authentication information of the sender imbedded as the electronic watermark from the authentication image and compares with authentication information of the sender with the feature information generated from the received electronic mail main text to authenticate the received electronic mail.
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