If you're really talking "least resistance", I see some ways:

• Render to SVG and then convert the SVG into a .png image using Inkscape. I've done this on Windows, and it works, as Inkscape can convert things from the command line. It might be that Inkscape wants a display even though it doesn't need it.
• Render to a JPG image using Imager. Imager is available on Windows as a PPM, other platforms hopefully provide you with a package manager for all the prerequisite libraries.
• Render to PostScript and use Ghostscript or ImageMagick+GhostScript to convert the PostScript to an image
• Render to a GIF or PNG image using GD