How do I find originals of photo files

If you imported photos to Photos while "Importing > Copy items to the Photos Library" has not been enabled, all photos you import with this option off have not been copied into your Photos Library. Perhaps they are still on the card of the camera where you took the photos with. Import them again.Referenced Photos will interfere with iCloud Photos.

You can find all photos you imported without copying them into the library with a smart album.

• File > New Smart album
• Set the rule to Photo > is > Referenced.

Is this album empty? If not, try to remember, where you imported the photos from and import them from there again.

If it was just optimization that's interfering it would start downloading the full sized version so you could use it for whatever.

Do you have an older Time Machine backup made before you first noticed this that you can restore (do now overwrite the current library) so to see if the same photos are missing.

In a managed library when photos are imported into the library the originals are copied into the library package. In a referenda library the photos are left where they were when imported and referenced to by the library. In that scenario if the source files are moved you'll get a missing file warning. Referenced libraries are strongly discouraged.

Are all of the photos giving that warning or just a few? If only a few it could be that the library was in referenced mode for a short time during those imports.

Check to see if you're running a "managed" or "referenced" library:

blackxacto wrote:

Should I have created the photo library designated as a system photo folder?

You can do that now with your primary working library. However, if you're using iCloud Library they your library IS a System Photo Library. Do you have "Optimize Mac Storage" enabled?