So I wanted to stamp a large number of photos with a watermark, so I could share printed copies with people.
ie.

I did it by using FastStone Image Viewer “Tools\Batch Convert Selected Images” option. I then clicked Advanced.
Notes on Font size:
| Image width in pixels | Font size | |
| 150 | 5 | |
| 450-900 | 16 | |
| 700-1200 | 24 | |
| 2400-6000 | 48 | |
| 6000-8000 | 72 |

