Abstract: An information carrier medium includes at least first and second sheet members (12, 14) each having first and second surfaces opposite to each other and laminated together with the first surface of the first sheet member bonded to the first surface of the second sheet member. A security indicium (14; 71) is formed on at least one of the first surfaces of the respective first and second sheet members (12, 14). The security indicium is made of at least one inking material of a kind capable of responding to a coherent light when irradiated thereby. An electro-optical reader for reading the security indicium (14; 71) is also disclosed.

Abstract: An image measuring apparatus for measuring an image of a tooth or gum applies the radiation of a laser beam to permit extremely quick, reliable, safe detection of dental caries and other dental pathological conditions. The low incident power of the laser radiation would not cause damage or pain to the tissue, such as the tooth or gum. The image measuring apparatus is equipped with a light source which emits light having at least a wavelength in a range of 500 nm or more to less than 600 nm; it uses the light emitted from the light source to obtain 2-dimensional images or computed tomographic images of a tooth or gum from the light, which has been transmitted through the tooth or gum, by using an optical heterodyne detection method.