Forgeryproof printed matter

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PROBLEM TO BE SOLVED : To obtain an ink for preventing counterfeit, capable of providing an image the counterfeit of which is extremely difficult by a commercial color copying machine or the like, capable of being produced at a low cost, and allowing the genuine one to be judged from the counterfeit one by using a simple device, and further to provide a printed product for preventing the counterfeit. SOLUTION : The genuineness of a printed product for preventing counterfeit is judged by observing the hues of reflected lights of both in the case of irradiating the object (the printed product) printed with an ink containing a lanthanoid rare earth compound with the sunlight or a light having the wave shape same as that of the sunlight, and the case irradiating the object with a light from a light source having emission characteristics in three wave length regions of blue (with 450 nm wave length), green (with 540 nm wave length) and red (with 610 wave length).