Abstract: A diffraction surface and a method of making the surface. The surface may be applied to labels and other items, to identify the original of the goods to which the label is attached. The surface can include a block grating. For example, the surface could include a plurality of blocks which adapted when illuminated will produce a recognisable image on an intercepting surface. The diffraction grating is manufactured by processing a data stream indicative of the image. Processing of the data stream includes obtaining a Fourier Transform of the data stream. Preferably, the data stream is clipped and quantised.