Photos and storage
How can I clean up my files and delete double copies of photos to make more room on my computer
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Are you asking about duplicate photos and videos in the Photos.app?
There should not be exact duplicates in Photos, as Photos will alert us, when we are trying to import identical image files twice. Also, when we are syncing exact duplicates between our devices with iCloud, photos will merge exactly identical images into one.
You may have similar images, however, differently edited versions of the same image, or or versions in a different format, or photos taken in a quick succession, showing the same scene. Or two identical images tagged differently with metadata, for example different locations or different date and time. that case it all be a matter of taste to decide, which version to keep. It is hard to do it automatically.
The next version of Photos, coming with macOS 13 Ventura will include a duplicate detector. I would wait for the release of Ventura - it is expected to be released this fall. You can save yourself a lot of work by waiting for the upgrade.
Be careful with third-party apps claiming to clean your Mac and remove duplicate files from inside Photos Libraries. They can damage the library badly, so you might lose all photos. Using third-party apps to remove duplicate photos might damage your Photos for macOS library - Apple Support
Only third-party apps, specifically designed for Photos, that are strictly using the programmatic interface to Photos are save to use, for example PowerPhotos. The mos recent version can even work with an iCloud Photos Library.