There is disclosed a method of encoding a latent image. The method comprises providing a latent image to be encoded, the latent image having a plurality of latent image elements, each latent image element having a visual characteristic which takes one of a predetermined set of values, providing a secondary pattern having a plurality of secondary image elements, the secondary pattern being capable of decoding the latent image once the latent image has been encoded, relating the latent image elements to the secondary image elements, and forming a primary pattern comprising a plurality of primary image elements which correspond to the secondary image elements displaced in accordance with the value of the visual characteristic of the latent image elements to which said secondary image elements are related. |