We have introduced an information embedding method on a digital watermark for a printing image and applied to thermal transfer printing. In this method, printed dots are arranged in staggered array to obtain area coverage modulation in each dot in thermal transfer printing. It is possible to correctly embed sub image information in this typical dot array and to electronically restore the sub image information. We confirmed that both invisibility characteristics and restoration characteristics are quite good and the digital watermarks can be normally embedded and restored as the result from the evaluations of 100 images printed at the resolution of 400 dpi after textual sub image information was embedded.