Decoding device, decoding method and decoding program

A decoding device has data extracting units extracting data from an image, data occurrence frequency calculating units calculating an occurrence frequency of data on a digit-by-digit basis, weighting units setting a weight corresponding to the occurrence frequency for every reference code so that the data with a smaller occurrence frequency in the extracted data becomes a majority in a decision by a weighted majority, first decision-by-majority units deciding the detection result of the data on the basis of the decision by the weighted majority, and judging units judging whether the image is falsified or non-falsified in accordance with whether the detection code decided by the first decision-by-majority units, is correct or erroneous.