An optical device , comprising; a colour shifting layer that exhibits different colours dependent on the angle of incidence of incident light, and; first and second arrays of at least partially transparent microstructures covering at least a part of the colour shifting layer and configured to modify the angle of light incident to, and reflected from, the colour shifting layer in order to generate a first optically variable effect, wherein; said first array of microstructures is arranged as a set of image elements (20-1, 20-2, 20-3) that cooperate to exhibit a first image, and; said second array of microstructures is arranged as a set of image elements (30-1, 30-2, 30-3) that cooperate to exhibit a second image, wherein; the image elements of the first array are interlaced with the image elements of the second array, and further wherein; the microstructures of the first and second arrays have at least one face that reflects incident light, whereby the microstructures of the first array are configured such that, when viewed along a first viewing direction the optical device exhibits the first image, and the microstructures of the second array are configured such that, when viewed along a second viewing direction the optical device exhibits the second image, wherein when viewed along the first viewing direction the microstructures of the first array appear brighter than their surroundings such that the optical device exhibits the first image, and when viewed along the second viewing direction the microstructures of the second array appear brighter than their surroundings such that the optical device exhibits the second image. a colour shifting layer that exhibits different colours dependent on the angle of incidence of incident light, and; first and second arrays of at least partially transparent microstructures covering at least a part of the colour shifting layer and configured to modify the angle of light incident to, and reflected from, the colour shifting layer in order to generate a first optically variable effect, wherein; said first array of microstructures is arranged as a set of image elements (20-1, 20-2, 20-3) that cooperate to exhibit a first image, and; said second array of microstructures is arranged as a set of image elements (30-1, 30-2, 30-3) that cooperate to exhibit a second image, wherein; the image elements of the first array are interlaced with the image elements of the second array, and further wherein; the microstructures of the first and second arrays have at least one face that reflects incident light, whereby the microstructures of the first array are configured such that, when viewed along a first viewing direction the optical device exhibits the first image, and the microstructures of the second array are configured such that, when viewed along a second viewing direction the optical device exhibits the second image, wherein when viewed along the first viewing direction the microstructures of the first array appear brighter than their surroundings such that the optical device exhibits the first image, and when viewed along the second viewing direction the microstructures of the second array appear brighter than their surroundings such that the optical device exhibits the second image. <EOS>