Apple planned to implement a system which scans all images stored on iPhone smartphones with the goal of finding illegal content to pass on to law enforcement agencies.
The difference between this system and the fact that user data is already scanned on the iCloud is the fact that this would be a system running directly on the end user’s own devices, a computer which they bought and own. This would be a service they never agreed to and which is forced onto them without control over it, on their own property.
The system itself is flawed in a way that malicious actors could for example place illegal content on a person’s device, leading to their unrightful prosecution.
archived source #1: https://wellthissucks.xyz/2021/08/05/apple-scans-all-images-on-iphones-archived-source-1/
source #2: https://www.hackerfactor.com/blog/index.php?/archives/929-One-Bad-Apple.html
archived source #2: https://wellthissucks.xyz/2021/08/08/apple-scans-all-images-on-iphones-archived-source-2/
source #3: https://www.lightbluetouchpaper.org/2021/10/15/bugs-in-our-pockets/
archived source #3: https://wellthissucks.xyz/2021/10/15/apple-scans-all-images-on-iphones-archived-source-3/