A security device includes: an elongate focusing structures array, the elongate axes are aligned along a first-direction, the elongate focusing structures parallel to one another periodically along a second-direction is orthogonally to the first-direction, each elongate focusing structure having an optical footprint of different elongate strips will be directed to the viewer in dependence on the viewing angle, the centre line of each optical footprint parallel with the first-direction; image elements-array overlapping the array of elongate focusing structures, the image elements-array representing elongate image slices of at least two respective images, each image slice including one or more image elements, and at least one image slice of each respective image in the optical footprint of each elongate focusing structure. The image elements-array is configured so the distance in the second-direction of each image slice from the centre line of an optical footprint in the image slice changes along the first-direction.