Susan - Glad you enjoyed the article.
Irfanview is what I use, but I have other photo editing programs that also have the ability to add text to a photo. It was software that came with my old camera.
Just make sure that you save the photo after inserting a few text lines. My computer went down (power outage in the neighborhod), so I had to redo it all over again. It is time consuming to initially do a large bed with many plants that you are labeling. But once it is done, it's great to have to refer to time and time again.