I'll post a little tk snippet later today, which exports a canvas full of text to png. (I'll have to make one up :-) ) Also I just noticed a new version of "pngwriter" was just announced on freshmeat.

About: The PNGwriter library, which requires libpng, allows you to plot to a 48-bit PNG file, saving it directly to disk. Plotting is as easy as specifying the red, green, and blue values and the x, y coordinates of the pixel. It includes functions for plotting simple geometric shapes (circle, rect, line), plotting text (UTF-8 support for Asian languages), reading the colour of a pixel, reading in a whole PNG file (great for image analysis), plotting and reading in HSV colourspace, and many others that might come in handy.

pngwriter