A security sheet including at least one paper substrate, at least one watermark produced in the paper substrate, the watermark having an exterior outline, at least one aperture of regular edge, produced by ablation of the paper substrate, and at least one security film that is at least partially superposed on the watermark and on the aperture. In the sheet, the at least one aperture lies inside the watermark, such as bounded by its exterior outline.

A security sheet including at least one paper substrate, at least one watermark produced in the paper substrate, the watermark having an exterior outline, at least one aperture of regular edge, produced by ablation of the paper substrate, and at least one security film that is at least partially superposed on the watermark and on the aperture. In the sheet, the at least one aperture lies inside the watermark, such as bounded by its exterior outline.

A prism layer has an uneven surface that includes at least one display region. An interface layer is adjacent to the uneven surface. The interface layer has a difference in refractive index from the prism layer such that a refractive index of a side of an interface between the uneven surface and the interface layer at which the prism layer is located is higher than a refractive index of a side of the interface at which the light interference layer is located. The display region includes inclination elements. The inclination elements adjacent to each other in an array direction contact each other in a plan view facing a plane along which the prism layer expands. The inclination elements include first inclination elements among which the inclination angle increases by the even angles along the array direction.

A prism layer has an uneven surface that includes at least one display region. An interface layer is adjacent to the uneven surface. The interface layer has a difference in refractive index from the prism layer such that a refractive index of a side of an interface between the uneven surface and the interface layer at which the prism layer is located is higher than a refractive index of a side of the interface at which the light interference layer is located. The display region includes inclination elements. The inclination elements adjacent to each other in an array direction contact each other in a plan view facing a plane along which the prism layer expands. The inclination elements include first inclination elements among which the inclination angle increases by the even angles along the array direction.

A phase modulation structure includes a recording surface including phase angle recording regions in a plurality of calculated element regions corresponding to reconstruction points of an image on a one-to-one basis, each phase angle recording region being formed of a plurality of unit blocks in each of which a phase angle is recorded, the phase angle being calculated based on a phase that is a sum of a plurality of phases of light from the corresponding reconstruction points; and a representative area that is one of divisions of the calculated element region, the representative area being obtained by radially dividing the calculated element region centered on a point on the calculated element region, the point being obtained by extending a normal line from the corresponding reconstruction point to the calculated element region on the recording surface.

A phase modulation structure includes a recording surface including phase angle recording regions in a plurality of calculated element regions corresponding to reconstruction points of an image on a one-to-one basis, each phase angle recording region being formed of a plurality of unit blocks in each of which a phase angle is recorded, the phase angle being calculated based on a phase that is a sum of a plurality of phases of light from the corresponding reconstruction points; and a representative area that is one of divisions of the calculated element region, the representative area being obtained by radially dividing the calculated element region centered on a point on the calculated element region, the point being obtained by extending a normal line from the corresponding reconstruction point to the calculated element region on the recording surface.

An optical device is formed by hot stamping a demetallized hologram to an optically variable foil or to a coating of optically variable ink. In another embodiment a hologram is hot stamped to a banknote or document printed with a color-shifting ink.

An optical device is formed by hot stamping a demetallized hologram to an optically variable foil or to a coating of optically variable ink. In another embodiment a hologram is hot stamped to a banknote or document printed with a color-shifting ink.

A hologram detection method according to an aspect of the disclosure, includes: inputting a first image, obtained by capturing a detection object on the basis of first flash intensity, to a neural network model to obtain a first detection result value representing the detection or not of a hologram for each of predetermined at least one detection unit regions; and comparing a threshold value with the first detection result value obtained for each detection unit region to determine the detection or not of a hologram in the first image and a first detection unit region where a hologram is detected.

A hologram detection method according to an aspect of the disclosure, includes: inputting a first image, obtained by capturing a detection object on the basis of first flash intensity, to a neural network model to obtain a first detection result value representing the detection or not of a hologram for each of predetermined at least one detection unit regions; and comparing a threshold value with the first detection result value obtained for each detection unit region to determine the detection or not of a hologram in the first image and a first detection unit region where a hologram is detected.