A method for preventing counterfeiting of an object (e.g. paper) is described. The method comprises capturing an image of at least a portion of the object, wherein the portion of the object whose image is captured is at least partially transparent, and wherein the captured image includes features of the internal structure of the object (e.g. the texture of the paper resulting from the arrangement of fibres from which the paper is made). The method further comprises generating, based on the image, a code that encodes features of the internal structure of the object, and recording the code. Generating the code may comprise applying a filter to the image to obtain a filtered image, and processing the filtered image to obtain a binary code. The filter may be a Gabor filter, and processing the filtered image may comprise applying a Gray code to the filtered image. The method may further comprise encrypting the binary code, and recording the code may comprise recording the encrypted binary code. A method for authenticating an object is also described. The method comprises capturing an image of at least a portion of the object, wherein the portion of the object whose image is captured is at least partially transparent, and wherein the captured image includes features of the internal structure of the object. The method further comprises generating, based on the image, a code that encodes features of the internal structure of the object, reading one or more reference values comprising at least a reference code, and authenticating the object based on the code and the reference code.