1. A method of authenticating a product, comprising: capturing an image of a product to be authenticated; determining a plurality of significant points of the captured image; comparing the plurality of significant points of the captured image of the product to be authenticated with a plurality of significant points of a previously captured reference image of a genuine product, wherein the product to be authenticated and the genuine product are located in a substantially similar position in the images from which the significant points are calculated; aligning a plurality of said significant points of the image of the product to be authenticated with a plurality of said significant points of the image of the genuine product prior to comparing the significant points, wherein comparing the plurality of significant points of the image of the product to be authenticated with the plurality of significant points of the image of the genuine product comprises determining if a significant point of the plurality of significant points of the image of the product to be authenticated is within a defined distance of a significant point of the plurality of significant points of the image of the genuine product; and determining a total number of significant points of the image of the product to be authenticated that are within said defined distance of a significant point of the image of the genuine product within a region of the image.