When you select a group of pictures to use in a Photos project, the pictures appear in an area below the project. You can drag the pictures one-by-one and place them where you want in the project, or you can click the Auto-Fill button just above the pictures. When you click the Auto-Fill button, Photos automatically places pictures into your project.
If you want this option turned off while you work on a project, follow these steps:
- Open the project.
- Control-click anywhere in the light-gray background of your project (the space surrounding the project's content).
- Click Enable Auto-fill Suggestions to turn off the option.
If you want to turn the auto-fill option back on, follow the same steps.