How to delete duplicate photos on a Mac

If your photos are in the Photos app, open Photos, click Duplicates under Utilities in the sidebar, select the rows you want, and click Merge. Photos keeps one copy and puts the others in Recently Deleted for 30 days. For photos in ordinary folders, edited or resized copies, and bursts, Photos' Duplicates album doesn't help, and that is where a duplicate finder comes in.

Step by step: the Duplicates album in Photos

Photos on a Mac finds duplicates by itself, from macOS Ventura onwards. These are Apple's steps, from its guide Remove duplicate photos and videos on Mac:

Open Photos on your Mac.
Click Duplicates under Utilities in the sidebar. If you can't see it, hold the pointer over Utilities and click the arrow beside it. On a large library the album can take a while to fill, because Photos analyses your pictures first.
Look at each row. Every row is one group of copies. Check them before you merge: you can select single items within a row rather than the whole row.
Select what to merge. Click a row, Shift-click or Command-click to add more, or press Command-A to select every row.
Click Merge and confirm. Photos leaves one copy where the group was.
Check Recently Deleted if you change your mind. The merged copies stay there for 30 days, and you can recover any of them in that time.

If you use an iCloud Shared Photo Library, choose Both Libraries from the Library menu in the toolbar first, or Photos only shows the duplicates in the library you are looking at.

Where Photos' Duplicates album stops

The Duplicates album is a good first step, and it costs nothing. It doesn't cover everything:

Only the Photos library. Copies in Downloads, an old backup, an export folder or an external drive are not in Photos, so it never sees them. Neither does Finder: macOS has no command that lists duplicate files in folders.
Copies that are not the same picture. A photo shrunk for email, cropped for a post, rotated or brightened is the same picture to you, but a different file. Look in the album before assuming it found them all.
Bursts and near-identical shots. Frames taken seconds apart are different photos, so they are not duplicates, yet they are often what fills a library.
Lightroom Classic and Capture One. Photos in a catalog are not in Photos. Deleting them in Finder breaks the catalog; see Lightroom Classic and Capture One for how to clear them safely.

Duplicate photos in folders and drives

Without an app, the manual way is slow but safe: open the folder in Finder, switch to List view, and sort by Name, then by Size. Copies often share a size, or a name with “copy” or a number on the end. Open each pair in Quick Look (press the Space bar) before you move one to the Trash, and empty the Trash only when you are sure.

That works for a handful of files. It doesn't find renamed copies in different folders, and it doesn't find edited ones at all.

With Folio Refresh

Folio Refresh is a duplicate photo finder for Mac. It scans the folders you choose, your Photos library, or a Lightroom Classic or Capture One catalog, on your Mac, and groups:

Exact copies, whatever they're called and wherever they are.
Edited, resized and cropped versions, labelled as alike rather than identical, so you check them.
Bursts and series, with the frame to keep suggested.

Every group suggests the copy to keep and says why. Then it clears them the way each place expects:

Folders: the copies you approve go to the Trash, and you can put any of them back.
Photos: they go into an album called “Folio Refresh Review”, for you to look over and delete in Photos. Folio Refresh deletes nothing there, and never marks a favourite.
Catalogs: duplicates are marked Rejected in Lightroom Classic or tagged Red in Capture One, after a backup and while the app is closed.

Nothing moves until you approve it, every group keeps at least one copy, and each photo is checked again just before it moves. Your photos are read on your Mac and never uploaded, and nothing is downloaded from iCloud unless you choose to. More on that in safe clean-up.

Before you start

Back up first. A recent Time Machine backup means nothing is ever truly lost, whichever way you clean up.
Keep the original. When two copies look the same, keep the larger file or the one you edited.
Empty the Trash and Recently Deleted last. Space only comes back once they're emptied, and that is the step you can't undo.

Price

Scanning and reviewing are free, and so are the first 100 photos you act on. Then $14.99 once, no subscription. macOS 15 Sequoia or later.