2001.07.09 13:49 "Re: Howto write a text ( endorse) into a tiff ? (maybe a little bit off-topic)", by Sim Zacks
With libtiff you can uncompress a tiff into the raw bits. You can then add text in it the same way you would a bitmap. It takes some programming, but it is not difficult. In windows it is easy to use the windows API I don't know any other OS's so I can;t tell you about their API's.
Without the API it gets a little more difficult because you basically have to figure out dot by dot how to draw the letters and then change the color of those pixels.