A method of illuminating an item is disclosed. The method includes applying adhesive to the item, interspersing a taggant in the adhesive, illuminating the item with an excitation signal, sensing luminescence emitted by the taggant in response to illumination by the excitation signal, and determining the authenticity of the item based on the sensed emitted luminescence. The item can include any item benefited by authentication, and can include a postage stamp. A method of customizing an item is disclosed. This can include the steps of preparing a substrate, applying a security feature to the substrate, printing non-customized information on the substrate, receiving image information, and printing the image information on the substrate.