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), 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.

WWW: http://pngwriter.sourceforge.net/