Still images or photos that are 4000 pixels wide or larger might not play back in some versions of iMovie for Mac. The images can be seen in the timeline, but they aren't visible in the preview window.
- Update to iMovie 10.1.1.
- Create a new event.
- Reimport your large images into the new event.
- If you used these images in any existing projects, open those projects, replace any broken images and re-save.
If you have not used these images before, create a new project using these images. Edit and save the project.
After you verify that the images appear in your project as expected, you can delete the older event clips that do not display correctly.