A method of printing a fluorescent image on a surface of a receiver medium comprises forming on the surface by a thermal dye transfer printing process a first image of a first fluorescent dye; and forming on the first image by a thermal dye transfer printing process a superimposed second image of a second fluorescent dye, the first and second dyes having different emission maxima. The method thus enables production of a non-monochrome fluorescent image (that can be substantially invisible in daylight but that is revealed on irradiation with ultraviolet (UV) light) that can be of substantially better quality than those produced by mass transfer printing processes. The method preferably involves the use of three different fluorescent dyes, for improved colour image quality. The invention also provides thermal transfer media suitable for use in the method and the resulting printed material bearing a fluorescent image.