A missing Duplicates collection does not tell you which photograph to delete. First check whether Photos has had the opportunity to finish indexing and detecting duplicates. Apple's missing Duplicates album guidance describes detection beginning with iOS 16 and requiring the iPhone to be locked and connected to power. Its duration depends on library size and background activity, so there is no guaranteed overnight deadline.
Find the collection for your version
Record the installed iOS version and open Apple's matching user guide. The duplicate-photo guide currently linked here uses a Collections and Utilities route; earlier interfaces can arrange those sections differently. Follow the version selector rather than assuming your screen must match a newer screenshot.
Confirm that the photographs you are comparing actually exist in the local Photos library. A file visible only in a chat or cloud-drive preview is a different starting point. If an intended photograph is missing entirely, locate that source first; waiting for duplicate detection does not retrieve an absent attachment.
Allow detection without creating more copies
Give the device a normal opportunity to perform its background work while locked and connected to power. Note a recent large import or other major library activity. Recheck the collection later without repeatedly importing the same files to force a result. Additional copies make the library harder to inspect and do not demonstrate that indexing has completed.
Apple also explains that the collection is absent when there are no duplicates to show. Two pictures that look similar to you are not proof that the system will group them. Do not infer an undocumented similarity threshold or promise that every crop, retouch or format conversion will be detected.
Inspect an actual pair independently
As a hypothetical example, a family saves a photograph from a group chat and later imports a larger source copy. Both look alike as thumbnails, but the collection is not yet visible. The family records the import and detection conditions, then inspects the two saved files individually if one is needed immediately. This is an assumed workflow, not a measured indexing time or a claim about Apple's grouping algorithm.
Compare the full pictures, dimensions and visible boundaries. A crop or a deliberately edited version may still be useful even if it resembles another image. When a group eventually appears, inspect it before any merge; the detection label does not decide which creative treatment the family wants.
Close the diagnosis with a clear result
Record either a detected group, a documented collection location, or an unresolved absence with the version and conditions checked. If still uncertain, use Apple's support route rather than resetting the library. Choose a verified working photograph for Imagild skills independently of cleanup. Acceptance here is a sound explanation of collection availability, not a promise that all visually similar photographs can be safely removed.