What the scan reads and never writes

You point Shutterfold at every photo and file you own. So here is exactly what the scan does with them.

What it reads

• Every file in each source you add. It reads the name and the size of each file.
• The contents of files that could be copies. Two files are copies only when they have the same size. So the scan reads only files that share a size with another file. It makes a fingerprint of the bytes (a BLAKE3 hash) and compares the fingerprints. The file name does not matter.
• In the Photos library, the originals on this Mac. It reads the original photos and videos, and leaves the library’s own database alone.
• In a Google Takeout export, the photos, videos and other files. It counts the .json files that Google adds beside each photo, and does not read them.

What it never does

• It never creates, changes, moves or deletes anything in a source.
• It never changes the date a file was last opened.
• It never downloads a file that is only in the cloud.
• It never writes its report into a source. The report goes into Shutterfold’s own folder on your Mac. See Uninstall for the place.
• It sends nothing from your files to us: no files, no names and no report. The privacy policy has the details.

Files that are only in the cloud

iCloud Drive, Google Drive, OneDrive, Dropbox and Box can keep a file in the cloud and show only its name on your Mac. The scan counts these files from their name and size. It never downloads them. It tells macOS to refuse a download on every read, so a read of a cloud-only file stops instead of fetching it.

Because the scan does not read these files, it cannot compare them. A cloud-only file with the same size as another file could be a copy. The report lists these as only in the cloud and not compared. Delete nothing there until they are compared.

To compare them today, make the folder available offline in the cloud app, wait for the download to finish, then scan again.

What it skips

The scan leaves some things out on purpose. The notes at the end of the report list each one.

• Hidden files and folders, whose names start with a dot.
• In your home folder, the Library and Applications folders. Apps keep their data there, and the cloud folders in Library are sources of their own.
• In your home folder, code projects: folders under version control, such as Git. Add one as its own source to read it in full.
• Software in any source: apps, caches, Python environments and installed packages.
• Files that Windows, Office and Finder make on their own, such as Thumbs.db.
• Empty files. There is nothing in them to compare.
• A Photos library inside another source. Add it as its own source.