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A secret management scheme in which important information is distributed to plural members of a group and then can be accessed only with the authorization under the agreements of the members, has been developed. A representative example is the thresholding scheme which is appropriate to apply to a group in which every member has equal accessing right because it has the structure that the secret information is fairly distributed. The encoding and decoding algorithm is commonly realized using a digital processor. Alternatively, it can also be realized by visual cryptography. The later is a good application of the thresholding scheme and has the advantageous characteristics that an exceptional algorithm is not to be needed for decryption. The only thing we have to do is piling up the key image on the encrypted image and confirming the decrypted image by the naked eye. The basic visual cryptograph can be simply realized by distributing an original image to two or more transparent papers.