If the graphic will be static and doesn't change based on user input or etc., you could just create a .grf out of it. I guess the easiest way to do that would be to export the image as a bitmap, open in paint, save as a .pcx file, and then open it in ZTools to convert to a hex .grf file. Then you can send the graphic to the printer along with your other ZPL code.
For examples on how to do this, I'll refer you to the ZPL programming guide, available at http://www.servopack.de/support/zebra/ZPLbasics.pdf
You'll find an example that explains creating and printing .grf files on page 36, and an example of sending both .grf and text to a label on page 63.