FALSE ALTERATION DETECTING METHOD, FALSE ALTERATION DETECTING PROGRAM, AND RECORDED MEDIUM ON WHICH THE PROGRAM IS RECORDED

摘要

A false alteration detecting method using an electronic watermark method of fragile type by number theoretic transform. A processing section sets parameters P, N, alpha of number theoretic transform (S101), and reads original image blocks fi,j (x,y) (S103), conducts number theoretic transform of fi,j(x,y) to calculate the number theoretic transform blocks Fi,j(x,y) (S105), determines the position (x',y') at which a signature image is to be embedded by using a randomizing function (S107), reads pixel values gi,j of the signature image for embedment from a storage section (S109), determines the embedment value delta of each block from the Fi,j (x',y') of the embedment position and gi,j (S111), adds the embedment value delta to the Fi,j(x,y) or subtracts the embedment value delta from the Fi,j(x,y) to determine the number theoretic transform blocks Hi,j(x,y) of the embedded image block (S113), calculates the inverse number theoretic transform of the Hi,j(x,y), determines the embedded image blocks hi,j(x,y), stores them, and outputs them to an output section.