The Storage Drain
If you own an iPhone and a Mac signed into the same Apple ID, Apple’s ecosystem strongly encourages utilizing iCloud Photos. By default, when you import photos from an SD card into the native macOS Photos application, or simply launch the app for the first time, macOS will automatically attempt to upload every single high-resolution image to your iCloud drive. While this ensures a unified camera roll across your devices, it will almost instantly consume your free 5GB iCloud storage tier. You will then be bombarded with daily, aggressive notifications across all your devices warning you that your “iCloud Storage is Full,” pressuring you into a paid monthly subscription.
Severing the Cloud Connection
To use the macOS Photos app purely as a local, offline photo manager and stop it from automatically attempting to upload gigabytes of data to Apple’s servers, you must disable the iCloud Photos sync feature.
Launch the Photos application on your Mac. In the top-left corner of the screen, click on the word Photos in the menu bar and select Settings (or Preferences). A new window will appear. Click on the iCloud tab at the very top of this window. You will see a large checkbox labelled iCloud Photos. If this box is checked, your Mac is actively trying to sync your library. Click the checkbox to remove the checkmark. A warning prompt may appear asking if you are sure you want to stop syncing and whether you want to download a copy of existing photos. Confirm your choice. From now on, any photos imported into your Mac will remain exclusively on your local hard drive.