everyday mac tools

The Photos library is taking up space: originals, caches and duplicates

· 6 min read

A Photos library that has grown to hundreds of gigabytes is almost always full of the obvious thing: original photos and, more often, original video. The thumbnails and previews inside it are real but they are a fraction of the total, and deleting them by hand is not something you should do.

Four ways to get the size down risk nothing: empty Recently Deleted, merge the duplicates Photos has already found, let iCloud hold the originals, or move the library to an external drive. Before any of them, check whether you have more than one library, because a forgotten second copy is the most common reason a Mac is full of photos.

Measure it, and check for a second library

Open Terminal and run du -sh ~/Pictures/*.

You are looking for two things: the size of Photos Library.photoslibrary, and whether there is anything else there, such as an old iPhoto Library or a second library left by a migration. A stale library is frequently tens of gigabytes for photos you already have in the live one.

To check what a suspect library holds, hold Option while opening Photos. You get a chooser listing every library it knows about, and opening one to look at it changes nothing.

If a library turns out to be redundant, drag it to the Trash and empty it. If you are not certain, copy it to an external drive first. Photos does not merge libraries for you, and there is no undo.

What is actually inside the package

The library is a package, so Finder shows it as one item. Right-click, Show Package Contents, and you get roughly:

  • originals, the actual imported files. This is nearly all of the weight.
  • resources, derivatives and thumbnails that Photos generates: the versions it shows you while browsing, and rendered copies of edits.
  • database, the library’s index of albums, faces, places, edits and everything else.

The rule about this view is that it is for looking, not for editing. Deleting anything inside the package by hand leaves the database referencing files that are not there, and the symptoms surface later as missing images. Finding the original of a photo inside the Photos library covers getting a file out safely.

If the derivatives have got out of proportion, the supported fix is to hold Option and Command while opening Photos, which offers to repair the library. On a large library that takes a long time.

The three deletions that are safe and immediate

Do these first, in this order.

  1. Empty Recently Deleted. In the Photos sidebar, under Utilities, Recently Deleted holds everything for 30 days by design. Open it and choose Delete All. This is the single most common reason a library does not shrink after a clear-out.
  2. Merge the duplicates Photos found. Also under Utilities, recent versions of Photos maintain a Duplicates album. It matches by content, so a photo imported twice at different sizes still appears, and merging keeps the highest quality version along with the keywords and albums from both. It is the one duplicate operation on a Mac you can run without much thought.
  3. Sort by size and look at the video. A minute of high-frame-rate video is worth hundreds of photos. Search for videos, sort largest first, and be honest about which forty-minute clips you will watch again.

A general duplicate finder should not be pointed inside a Photos library. It cannot see the database, so removing a file it considers redundant breaks the library’s reference to it. Use Photos’ own Duplicates album for photos, and keep general tools for the rest of the disk. Finding duplicate files without deleting the wrong copy covers that distinction in more detail.

Let iCloud hold the originals

If iCloud Photos is on, Photos can keep full-resolution originals in iCloud and leave smaller versions on the Mac, downloading an original when you open or export it.

Open Photos, Settings, then the iCloud tab. With iCloud Photos enabled you choose between Download Originals to this Mac and Optimize Mac Storage. Switching to Optimize is the largest single reduction available on most Macs, and it happens gradually.

Three things to be clear about before you do it:

  • It only evicts originals when the disk is under pressure, so nothing may happen on the day you turn it on.
  • Your Mac stops being a complete local copy. If that Mac was your backup, it is not any more, and iCloud is sync rather than backup: a photo deleted on the Mac is deleted everywhere.
  • Editing or exporting an original requires a connection.

Optimize Mac Storage in iCloud covers exactly what it evicts and when, including the backup catch, which is the part people find out about later.

If you want the whole library kept locally and safe, the alternative is the next section.

Move the library to an external drive

This keeps every original, gets it off the internal disk, and is fully supported.

  1. Quit Photos.
  2. Copy Photos Library.photoslibrary from ~/Pictures to the external drive. Copy, do not move, until you have confirmed the copy works.
  3. Hold Option and open Photos, choose Other Library, and select the copy on the external drive.
  4. Once it opens and looks right, go to Photos, Settings, General and click Use as System Photo Library. Without this step, iCloud Photos and the Photos widget keep pointing at the old one.
  5. Confirm everything is present, then delete the original from ~/Pictures.

The drive must be formatted APFS or Mac OS Extended; a library on an exFAT drive will misbehave. And with iCloud Photos on, the drive has to be attached for syncing, which argues for a drive that lives on the desk rather than one that travels.

Where the rest of the photo weight hides

The library is not the only place photos accumulate. Copying images off a phone by hand leaves a second set in Downloads. Photos people sent you are stored separately, in the Messages attachments folder, and can run to several gigabytes. And screenshots, unglamorous but numerous, pile up wherever you pointed them.

If you are not sure whether Photos is even your biggest item, an audit answers that faster than another evening in Finder. Crumb reads the whole Mac read-only and breaks System Data into its parts, alongside local snapshots and old iOS backups, with the total shown before anything is removed. It is not a photo tool and it will not go inside a Photos library, which is the correct behavior; what it tells you is whether the library is your problem or a distraction from it. The audit and one full cleanup are free.

Questions

If I delete photos on the Mac, do they go from my iPhone? With iCloud Photos on, yes, and they land in Recently Deleted on every device for 30 days. With iCloud Photos off, the Mac library is independent.

Why is the library still huge after I deleted thousands of photos? Recently Deleted, almost always. After emptying it, give macOS time: freed blocks can be counted as purgeable rather than free for a while. Purgeable space on a Mac explains that gap.

Can I delete the thumbnails and previews inside the package? No. They regenerate, but not on demand and not without the database being rebuilt, and hand-deleting inside the package is how libraries end up with missing images. Repair the library instead.

Is Optimize Mac Storage the same as a backup? No, and the confusion is expensive. It is a sync arrangement: what is on the Mac and what is in iCloud are one collection, so a deletion propagates. Keep a separate backup if these photos matter.