Simultaneously with a robust watermark and fragile watermark or semi-watermark is embedded into conventional securities, etc., such as gift coupon, various kinds of ticket, coupon, electronic stamp, bond & debenture, note, stock certificate, lottery, paper money, check, etc. and various kinds of public documents including certificates, etc. requiring confirmation and authentication (hereinafter, referred to as "securities, etc.") in the form of digital file. Such watermark-embedded securities, etc. are conveniently issued on-line and are printed out in the form of paper through a printer. The printed securities, etc. are used off-line and are authenticated by determining the forgery or alternation by means of photocopy, etc. through the detection of the embedded watermark.