1. A method for integrating a synthetic hologram in a directly observable image of a scene, comprising the steps of: defining a first image (IMAGE_G) of said scene, comprising grayscale pixels; forming first and second matrixes from the first image, the first matrix (IMAGE_G B&W ) comprising pixels of a first and of a second shade according to whether the corresponding pixel of the first image (IMAGE_G) has a gray level greater than or smaller than a threshold (α), each element of the second matrix (IMAGE_G′) comprising a value equal to the gray level difference between the corresponding pixel of the first image (IMAGE_G) and the corresponding pixel of the first matrix (IMAGE_G B&W ); forming a third pixel matrix (φ H ) by calculating the phase image of the Fourier transform of an image originating from a second source image of the hologram (IMAGE_H); forming a fourth pixel matrix (IMAGE_F), each pixel of the fourth matrix comprising a central area having its surface area determined based on the corresponding element of the second matrix (IMAGE_G′) and off-centered in the pixel according to the corresponding pixel of the third matrix (φ H ); and performing a lithography of an opaque layer at the surface of a wafer according to the pattern defined by the fourth pixel matrix (IMAGE_F), the lithography being provided to remove, from a pixel, the opaque layer inside of the central area if the equivalent pixel of the first matrix (IMAGE_G B&W ) is of the first shade and to remove the opaque layer outside of the central area if the equivalent pixel of the first matrix (IMAGE_G B&W ) is of the second shade.