Duplicate photos of entire photo library

Where are you seeing the copies? Inside the Photos Library package?

Photos is creating working copies for each image file you import for a faster browsing. This is normal and necessary. There are thumbnails, previews, detected faces, items for the media browser in different folders. Many of these files are looking like duplicates of the same size as the original, but are actually clones or hard links and are stored efficiently and not needing extra storage. If you are no longer using "Optimise storage", you will need storage for the original image files plus the storage for the previews of the image files that have been edited.

If the originals are HEIC files, or HEVC you will need the additional storage for a version in a more compatible format. Would it be possible for you to upgrade to Big Sur and Photos 6? In Photos 6 are currently no longer JPEG previews for HEIC files created and it is saving a lot of storage. However, we are no longer seeing the HEICs in the Media Browser in other apps.

Are the two versions of the photo shown side-by-side in All Photos? Could it be, that you have enabled my Photo Stream? The My Photo Stream photos are also shown in All Photos.

You may want to compare the Info for the apparent duplicates. Are the filenames the same, the file type (both are JPEGs for example), is the pixel size the same and the file size?

You may want to enable all badge overlays in the View menu: "View > Metadata". Set all checkmarks there, so you can tell by the badges on the thumbnails, if one of the versions has been edited, for example.

One more question, if you do not mind: When you changed the preferences for iCloud and disabled "Optimise Storage", did you do this while viewing the same Photos Library as before? You can see the path to your current Photos Library in the Photos Preferences > General > Path to Photos Library.

When looking at the metadata, the duplicates have the exact same time stamp but one is HEIF and the other is JPEG, and they are different file sizes.

A JPEG has twice the file size of a HEIC file of the same quality. HEIC has a better compression algorithm.

If your iPhone is set to shoot the photos in the high efficiency format HEIC, please check the Settings on your iPhone for the transfer to a computer. You will create JPEG duplicates by downloading the the photos as JPEGs from the iPhone by manually downloading. Using HEIF or HEVC media on Apple devices - Apple Support

• Check "Settings > Camera > Formats". Is it set to "High Efficiency"? Then you are using the space saving HEIF on the iPhone, which is supported on a Mac with macOS 10.15
• Check "Settings > Photos > Transfer to Mac or PC. Is it set to "Most Compatible"? If yes, that is the setting that is creating the additional JPEGS, when you download the photos manually from your Mac. I would change it back to "Keep originals".

The problem is, that iCloud is syncing the HEIC files to your Mac, and when you download the images manually, you are importing additional JPEGS because of the "Transfer to Mac or PC" setting.

The switch determines whether the full-resolution versions of the photos are kept on the Mac all of the time or only when free storage is not scarce. The other resolutions should be in the library package all of the time, but only one copy of each photo should display through the Photos application.

Hi

Is the download sync complete. What does it say about sync status at the bottom of the all photos view? Here is mine (updated just now):

You don't have a top strip reading Years, Months, Days, All Photos over the grid of pictures in the Photos view under Library in the left sidebar?

Is it possible that you have used a cable connection to import photos directly from your iPhone to your Mac? Combining different transfer methods (iCloud Photos, My Photo Stream, direct cable import) between the same pair of devices can cause confusion such as you describe. They don't follow the same rules on what the result is called, interfering with duplicate detection.

Automatic will convert HEIC format to JPG Format on download if needed for compatibility with your mac.

Keep original will transfer the file unchanged.

IF automatic has been converting files on download, then every time you connect via a cable those files will not be recognised as duplicates and will download again.

Hi

If you are looking inside the library package - I strongly recommended you stop. If you delete anything from there, or edit anything, you will damage the library and potentially lose access to all your photos. It is a data structure not intended for the end user to play with - that is why the contents are hidden by default.

Leonie has provided an explanation of why there are multiple versions of the same image inside the library package.