Method to authenticate a substrate using speckle patterns and a device to perform the method

A method to authenticate a substrate based on unique microstructure inherent to a region of interest of a substrate surface of the substrate, the method comprising:

• a. emitting photons from a light source onto the region of interest;
• b. emitting ultrasound waves from an ultrasound source onto the region of interest;
• c. capturing at least one photo acoustic speckle image of the region of interest by capturing a light image from the emitted photons in the presence of the emitted ultrasound to obtain the at least one captured photo acoustic speckle image of the region of interest;
• and
• d. comparing the at least one captured photo acoustic speckle image with at least one reference in order to determine authenticity of the substrate,
• wherein step d further comprises:
• e. extracting a plurality of specific features from the at least one captured image;
• f. identifying the location of each specific feature;
• and
• g. comparing the identified locations with reference identified locations from an at least one reference image previously taken from the region of interest and stored in a database.