A security device is disclosed including a substrate and one or more focusing elements or lens structures located on one side of the substrate. The security device includes a plurality of picture elements connected to each focusing element, the picture elements including at least a first and second group of picture elements. Each picture element can consist of pixels that are located in an object plane that can be viewed through the connected focusing element. Each picture element comprises a diffractive grating element or sub-wavelength grating element which, when illuminated by a light source, produces a diffraction image which can be viewed in a range of viewing angles around the device. Image elements of the first group are visible in a first range of viewing angles and image elements of the second group are visible in a second range of viewing angles. The security device is particularly suitable for use on security documents such as banknotes. A method of forming a security device is also disclosed.
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