It sounds like you did an "Insert", "Picture", "From file" method to insert
the image on your master slide. Try this:
1. Delete the image (assuming you still have the image file somewhere) from
your slide master.
2. Click "Format", "Background", click the dropdown and select "Fill
Effects".
3. Click the "Picture" TAB, then "Select Picture".
4. Browse to your image file, select it, then click "Insert".
5. Click "OK", then click "Apply to all".
6. Close out of your Slide Master and try doing a print job using "Pure
black and white".
I'm interested in the results so post back if possible.