We have developed a neural network (NN) recognition and its hardware for paper currency. We have proposed mask concept to extract characteristics of the currency. Here, we propose a unique mask which has a symmetrical masked area against axes which divide a long side and short one of the currency. We can obtain the same value from both upright image and inverse one of the currency using the axis-symmetrical mask. This means that these values are invariant to upright and inverse of the currency

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... onveyance. Namely, we can recognize twice number of currency kinds compared with the conventional mask though the NN construction is the same. Furthermore, we optimized the axis-symmetrical mask by genetic algorithm. Finally, we show the effectiveness of the optimization by statistical analysis of mask processed values.