Direct thermal and thermal transfer printing methods can be used for creating documents with embedded permanent images and texts as security codes, which are visible only under ultraviolet light. Copying or scanning of the documents cannot reproduce these images. Such documents can be created by direct thermal printing of single sheets, containing single or multi-layer coatings of image forming components, by single or multi-pass printing. A combination of direct thermal and thermal transfer methods can also be used for generating similar documents by single-pass printing.Single sheet direct thermal process, in which the printed images gradually fade with time, can be used for creating documents for temporary identification. The length of time required for such fading can be controlled by proper selection of the components of the imaging systems.