How to Find Duplicate Photos on a Mac

What the Photos app catches

Open Photos, look in the sidebar under Utilities, and Duplicates shows up if any exist. It finds photos that are exactly identical, or that were imported twice from the same source, the same photo synced from two devices, or reimported from an old backup. That's a real and useful case.

What it doesn't catch is anything that isn't a pixel-for-pixel match. That's most of what clutters a photo library.

The gap: near-duplicates

• Burst shots. Ten frames of the same moment, one keeper and nine you'll never look at again, each one a distinct file with no exact match among them.
• Slight retakes. Three photos of the same scene a second apart, someone blinked in one.
• Edited versions. A photo and its cropped or filtered copy are different files at the pixel level, so an exact-match tool sees no relationship between them at all.

None of these are duplicates in the strict sense the Photos app checks for, and all of them are the actual junk filling up a photo library. This is a harder problem than file deduplication: it requires understanding visual similarity, not just comparing bytes.

The manual approach

Sort by date, scroll through, and eyeball anything shot within the same few seconds. It works. It's also slow on a library with years of photos in it, and it's the kind of task that's easy to start and never finish, which is exactly why most people's Photos libraries have thousands of near-duplicates sitting untouched.

For anything that isn't a photo, exact byte-for-byte duplicates in Documents or Downloads, the approach is different again. Covered in finding duplicate files.