Method for manufacturing a security device , comprising the following steps: - obtaining (S300) 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 (S310) at least a first and a second grayscale image (IM1-IMn) from said digital colour image : -- said first grayscale image (IM1) 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 (IM2) 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 (S310) a third and/or a fourth grayscale image (IM1-IMn) from said digital colour image : - said third grayscale image (IM3) 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 (IM4) 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 (S320) 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 (S300) 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 (S310) at least a first and a second grayscale image (IM1-IMn) from said digital colour image : -- said first grayscale image (IM1) 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 (IM2) 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 (IM1) 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 (IM2) 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 (S310) a third and/or a fourth grayscale image (IM1-IMn) from said digital colour image : - said third grayscale image (IM3) 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 (IM4) 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 (S320) 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. <EOS>