Disclosed is a method of detecting a predetermined mark embedded in an image. The mark (29) comprises a predetermined arrangement of a plurality of elements (30), each element having a predetermined colour characteristic and predetermined shape. The method processes (20) the image to provide an encoded representation of the image at a predetermined resolution (eg. 200 dpi). The coordinate positions for substantially each of the elements of the mark embedded in the image are detected (22), wherein the detection is characterised by applying at least one mask (80) to substantially each pixel of the encoded representation. From the coordinate positions, a set of spatial features representing a spatial arrangement of the detected elements are then determined (23). The determined set of spatial features is then compared (24) to a known set of spatial features to provide a confidence level measure for a degree of matching between the known set and the determined set of spatial features.