1. A security device, comprising: an array of focusing elements, each focusing element being adapted to focus light in at least a first direction, the focusing elements being arranged on a regular grid in at least one dimension; and an array of image elements overlapping the array of focusing elements, the image elements being arranged based on a repeating unit cell defining image element positions, the periodicity of the unit cells being substantially the same as that of the grid on which the array of focusing elements is arranged, the unit cell defining a set of image element positions therewithin, each image element position within the unit cell being assigned to carry an image element of a respective corresponding image; whereby, depending on the viewing angle, the array of focusing elements directs light from selected image element positions to the viewer, such that as the device is tilted different ones of the respective images are displayed by the image elements at the selected image element positions in combination, sequentially; wherein a center area of each unit cell, comprising one or more image element positions, is provided with one or more image elements of a corresponding center image, the center area being larger than each outer area of the unit cell, the outer areas being located outside the center area and provided with image elements of other respective images defined by the array of image elements, such that a first range of viewing angles, over which the center image is displayed to a viewer, is greater than a range of viewing angles over which each other image is displayed, and wherein an appearance of the security device remains static over the first range of viewing angles.