Method for manufacturing a security device, comprising the following steps: - obtaining a digital colour image, said digital colour image comprising a plurality of pixels (P1-Pp), the colour of each pixel (P1-Pp) being defined in accordance with at least a first, a second and a third colour component of a colour space, - obtaining at least a first and a second grayscale image (IM1-IMn) from said digital colour image: -- said first grayscale image comprising a plurality of pixels each having a grayscale level representing the first colour component of the corresponding pixel of the digital colour image, and -- said second grayscale image comprising a plurality of pixels each having a grayscale level representing the second colour component of the corresponding pixel of the digital colour image, - obtaining a third and/or a fourth grayscale image (IM1-IMn) from said digital colour image: - said third grayscale image comprising a plurality of pixels each having a grayscale level representing the third colour component of the corresponding pixel of the digital colour image, and - said fourth grayscale image comprising a plurality of pixels each having a grayscale level representing the first, second and third colour components of the corresponding pixel of the digital colour image, - forming said at least first and second grayscale images (IM1-IMn) on a physical medium of said security device, and forming said third grayscale image and/or said fourth grayscale image on the physical medium of said security device, the method being characterized in that said at least first, second, third and/or fourth grayscale images (IM1-IMn) are formed on the physical medium of the security device by laser etching. - obtaining a digital colour image, said digital colour image comprising a plurality of pixels (P1-Pp), the colour of each pixel (P1-Pp) being defined in accordance with at least a first, a second and a third colour component of a colour space, - obtaining at least a first and a second grayscale image (IM1-IMn) from said digital colour image: -- said first grayscale image comprising a plurality of pixels each having a grayscale level representing the first colour component of the corresponding pixel of the digital colour image, and -- said second grayscale image comprising a plurality of pixels each having a grayscale level representing the second colour component of the corresponding pixel of the digital colour image, -- said first grayscale image comprising a plurality of pixels each having a grayscale level representing the first colour component of the corresponding pixel of the digital colour image, and -- said second grayscale image comprising a plurality of pixels each having a grayscale level representing the second colour component of the corresponding pixel of the digital colour image, - obtaining a third and/or a fourth grayscale image (IM1-IMn) from said digital colour image: - said third grayscale image comprising a plurality of pixels each having a grayscale level representing the third colour component of the corresponding pixel of the digital colour image, and - said fourth grayscale image comprising a plurality of pixels each having a grayscale level representing the first, second and third colour components of the corresponding pixel of the digital colour image, - forming said at least first and second grayscale images (IM1-IMn) on a physical medium of said security device, and forming said third grayscale image and/or said fourth grayscale image on the physical medium of said security device, the method being characterized in that said at least first, second, third and/or fourth grayscale images (IM1-IMn) are formed on the physical medium of the security device by laser etching.