I've never noticed a problem reading the text on your photos, but even though these photos make it very easy to read your notes, the box may sometimes block some important detail in the photos, so the text only version might prove better in these cases. Your explanations and photos have always been great and easy to understand.
There may be times when putting the text in a box might be a better choice, but it may not always be the best way. I think you should choose based on the photo and text that you are combining and use whichever way is most appropriate for that photo. Changing the color of the text to achieve a significant contrast difference between the photo background and the text also works well. You past choice of yellow has worked well in most cases.
Keep up the great work Harry. Your woodworking, teaching, and photography skills are tops in my book.
Central North Carolina