A seal carving apparatus includes a thermal head having a plurality of heat generating elements disposed in lines, and thermal drive control means that performs a control process of selectively and thermally driving the individual heat generating elements while moving the thermal head and a porous material in relative to each other with the thermal head being in abutment with the porous material, thereby forming a seal face on the porous material. The thermal drive control means controls a pulse time width for thermally driving the individual heat generating elements of the thermal head under pulse width modulation control based on gradation image data having a gradation value, thereby forming a seal with a gradation on the porous material.

A method of illumating 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.