Once I’ve made the movie can I delete the photo in photos or will that also delete it from the movie?

Photos app photos and videos that are used in an iMovie project are full sized duplicates of the originals that are in the Photos app library. That media is stored in a finder folder in the iMovie library. Thus, the photos and videos are independent of their original counterparts in the Photos app library. You can delete them from the Photos app library and the duplicate originals will remain in iMovie unless you manually delete them from the iMovie library.

Further, the movies that are shared out (exported) from an iMovie project are standalone files that are not affected by any deletions of the source media either from iMovie, the Photos app, or the Finder.

-- Rich

Adding to my previous post, if you want to preserve, organize, and/or access your media it may not be advisable to delete your source media from its original location outside of iMovie. It can be awkward to retrieve your media from iMovie in case you want to use it elsewhere. And while iMovie has some decent organizing capabilities, it is nowhere near as versatile as the Photos app organizing tools -- where you can create albums, including smart albums, add and sort by keywords, search by title or keyword, etc. Finally, the iMovie app is constantly evolving and iMovie libraries can become corrupted, so you don't want the sole location of your original photos to be the iMovie system (or any other app's system, for that matter). In addition to the Photos app library I keep all of my photos, double backed up, in finder folders organized by year. That way they are out of the Photos app system or iMovie system, in case for some reason those apps become corrupted.

-- Rich

You are welcome. Happy that I could help.

-- Rich