A printing apparatus includes a magnetic rotatable roller with a smooth even outer surface for aligning magnetic flakes in a carrier, such as an ink vehicle or a paint vehicle to create optically variable images in a high-speed, linear printing operation. Images can provide security features on high-value documents, such as bank notes. Magnetic flakes in the ink are aligned using magnetic portions of the roller, that can be formed by permanent magnets embedded in a non-magnetic roller body, or selectively magnetized portions of a flexible magnetic cover of the roller. In some embodiments, the roller is assembled for a plurality of interchangeable sections, which can include spinning magnets. Selected orientation of the magnetic pigment flakes can achieve a variety of illusive optical effects that are useful for decorative or security applications.