Adding photos to your journal is not just a great way of tracking your garden's progress; they also help trigger your memory months and years after your journal was started.
As your garden starts to grow, snap and print shots of great combinations and favorite scenes. You can shoot the same area at different times, to see the progression. Take shots of containers you'd like to duplicate. Try the old Black and White photo trick, to see how things look without the distraction of color.
Photos are a nice place to jot notes about plants that need dividing or moving and colors that clash or just aren't right.
Photograph pests and diseases, to keep track of problems. And don't forget to take shots of problem areas, to study and correct during the off season. No one has to see them but you.