Shiny or reflective portions of a product surface, such as areas covered by foil, are represented to a user viewing a product image by a looped animation that simulates the visual effect of light on those reflective portions. The animation comprises a sequence of images generated by applying a gradient function to an image of the areas corresponding to the reflective portions of the product. To generate the individual images for use in the animation, the gradient function is applied at different offset positions relative to the product image.