A photograph in a Shared Album may need a crop or correction for your own project. Before editing it, identify the copy you are changing and whether the owner expects a revised version to be posted. A local editing decision and a shared publication decision should be explicit.

This guide concerns Shared Albums in Photos on Mac. iCloud Shared Photo Library is a different feature with different contribution rules. Check the feature name in the sidebar and begin with one image whose owner and intended use you understand.

To save a Shared Album item locally, open the album, select the item, Control-click and choose Import. It appears in your library and Imports. Apple explains that editing this imported copy does not change the original photograph in the Shared Album.

You can also open the shared image, click Edit and then Import before editing. Sharing the edited local version back through Share, Shared Albums adds that revised image to the album while the original remains there. It does not silently replace the original post.

Verify the local edit before discussing a repost

Make the intended correction in the imported copy and inspect the result in your library. Then return to the Shared Album and compare the original post. Keep the two roles clear in your notes: the shared reference and the local working revision.

If the revision is for a private document only, a repost may be unnecessary. If other participants need it, agree on how the revision will be identified so they do not mistake two visible versions for unrelated photographs or choose the outdated one.

Before any authorised repost, check the complete frame and any visible information the correction might reveal or obscure. Confirm that the revised picture still represents the intended event accurately and that the owner is comfortable with its shared use.

Treat replacement and removal as separate decisions

After an authorised repost, inspect the album from the intended participant view and identify both versions. Decide with the album owner whether the original should remain for context. Do not assume local editing has withdrawn the earlier image or that removing a shared post retracts copies somebody already saved.

Keep the source and working revision until the delivery has been accepted. A short version note can explain the correction without forcing future editors to infer which image is current from subtle visual differences. The useful outcome is a clearly identified revision with its sharing scope understood.

Reference: Apple: items and edits in Shared Albums.