| 摘要 |
PURPOSE:To facilitate the detection of information and to prevent the forging of the information by recording the information on the surface of recording medium with general paints, and recording the other information near said recording medium with infrared ray absorbing paints to detect this infrared ray. CONSTITUTION:On a car number-plate (a), a ground-color 11 is displayed in white, a car-number 12 in green, a bar-code 13 in black infrared ray absorbing paints. When the car passes through a car detecting device 1, the infrared ray discharged from an optical filter 5 irradiates the surface of the plate (a), and by picking up its reflection light, a picture is obtained whose ground-color 11 and the number 2 part become white and the part of the code 13 becomes black in an image pickup device 2. Thus, even if the number 12 is forged, scanning the paints painted on the code 13 with the image pickup device which has sensitivity adjusted to the wavelength region of the infrared ray from the filter 5, can detect without fail compared with the code 13 which is displayed corresponding to the number 12.
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