With the recent release of operating system updates, you might see a message like this in Photos in macOS:
The original image was captured in an unsupported image format. To view the full-resolution photo you need to upgrade to the latest version of macOS.
It’s a new one, unique to asymmetric upgrading! If you move your iPhone or iPad to iOS 11, change a setting, and keep a Mac running macOS 10.12 Sierra or earlier, you can wind up with files syncing across iCloud that Photos for macOS can display previews of, but not manipulate.
iOS 11 and macOS 10.13 High Sierra add support for two super-efficient image and video file formats: HEIF and HEVC. By default, iOS 11 cameras shoot in formats that are backwards compatible. However, you can change this in Settings > Camera > Formats by switching Most Compatible to High Efficiency.
iOS 11 can still export and share files by converting them, which it does automatically. But iCloud Photo Library sync copies the exact file.
Apple has no plans to update older versions of Photos, so you’ll need High Sierra and its updated version of Photos to work directly with the new formats.
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