Basics, hand drawn:

1. Get image into Preview (sample Ararat here)
2. Export as PNG
3. Reopen.
4. Adjust using “Tools > Adjust Color…”
   1. Increase contrast
   2. Invert image by swapping white point and black point
5. Use “Instant Alpha” to select and then delete background (easiest if “Preferences > Background” is green)
6. Re-export as PNG

Basics, typeset in a word processor:

1. Set type (white text in a green colored text box is easiest).
2. Export as pdf.
3. Open in Preview.
4. Export as PNG.
5. Reopen.
6. Adjust using “Tools > Adjust Color…” if type is not white.
   1. Increase contrast
   2. Invert image by swapping white point and black point
7. Use “Instant Alpha” to select and then delete background (easiest if “Preferences > Background” is green)
8. Re-export as PNG