Add media from your photo library in iMovie on Mac
All the photos and video clips in your Photos, iPhoto, and Aperture libraries are automatically available for use in iMovie.
Note: You can’t use Aperture or iPhoto in versions of the Mac operating system after macOS Mojave 10.14. If your photos are in an Aperture or iPhoto library, you can update your photo library to Photos. See the Apple Support article Migrate your Aperture libraries to Photos or Adobe Lightroom Classic.
In the iMovie app on your Mac, select your photo library in the Libraries list.
Click the pop-up menu at the top of the browser, choose a content category, and then scroll through the thumbnails of photos and video clips in that category.
Select the photo or clip you want to use to see a preview in the viewer.
Do one of the following:
Insert the photo or video clip: Drag it to the timeline between clips or between a clip and a transition.
As you drag, a blue box appears in the timeline, indicating where the photo or clip will appear in the timeline.
Replace a clip: Drag the photo or clip on top of a clip in the timeline.
As you drag, a white border appears around the clip in the timeline. When you release the mouse button, choose Replace from the menu that appears. The photo or clip replaces the clip in the timeline.