A method to authenticate a product with an imaging device, the imaging device being a digital scanner, a digital camera, or a mobile phone with an integrated camera, the product surface having a microstructure, the microstructure having a statistical property of noise, the method comprising an acquisition phase and an identification phase, the acquisition phase comprising: • Lighting, with a lighting source, the surface of a reference product item from an incidence angle direction to produce a specular reflection of light from the product surface microstructure; • Digitally acquiring, with the imaging device, a two-dimensional template image of the reference product surface by sampling on a uniformly spaced orthogonal grid of at least one color component; • Preprocessing the template image in order to remove its macroscopic variations by applying a flattening function on the template image, the flattening function generating a difference between an image and its frequency low-passed version; • Storing in a reference database the preprocessed template image; the identification phase comprising: • Lighting, with the lighting source, the surface of a product item to be authenticated, from an incidence angle direction to produce a specular reflection of light from the product surface microstructure imperfections; • Digitally acquiring, with the imaging device, a two-dimensional snapshot image of the product surface by sampling on a uniformly spaced orthogonal grid of at least one color component; • Preprocessing the snapshot image in order to remove macroscopic color variations by applying the flattening function on the captured snapshot image; • Comparing the preprocessed snapshot image and the stored preprocessed template image by determining a matching metric, and authenticating the product item if the matching metric is above a predefined level. • Lighting, with a lighting source, the surface of a reference product item from an incidence angle direction to produce a specular reflection of light from the product surface microstructure; • Digitally acquiring, with the imaging device, a two-dimensional template image of the reference product surface by sampling on a uniformly spaced orthogonal grid of at least one color component; • Preprocessing the template image in order to remove its macroscopic variations by applying a flattening function on the template image, the flattening function generating a difference between an image and its frequency low-passed version; • Storing in a reference database the preprocessed template image; • Lighting, with the lighting source, the surface of a product item to be authenticated, from an incidence angle direction to produce a specular reflection of light from the product surface microstructure imperfections; • Digitally acquiring, with the imaging device, a two-dimensional snapshot image of the product surface by sampling on a uniformly spaced orthogonal grid of at least one color component; • Preprocessing the snapshot image in order to remove macroscopic color variations by applying the flattening function on the captured snapshot image; • Comparing the preprocessed snapshot image and the stored preprocessed template image by determining a matching metric, and authenticating the product item if the matching metric is above a predefined level.