...but we do not trust you, so we do store that database on your device and check every picture, you are uploading to our servers. You might be a liar, so you will get checked on every upload, slomojoe. If there is a false alarm, we will review your images and approve them. You will not notice that, if you are not cheating on us. We will not tell you about your private pictures, our clerks were glaring at (...nice butt btw.) So just sit back and relax.you are incorrect
having the database on device gives more security to the end user not less, anything done "in the cloud" or on apple's servers is completely blind to us the users, images could be added willy nilly, the database could changed and we the user would have no idea what is taking place
apple is specifically placing the database on-device because it gives us the users more transparency,
1) it is put on device only with a signed operating system
2) no remote updates are possible this ensures that the same database is every phone worldwide
3) this prevents apple from replacing the database with another database
4) apple will provide a root hash with every database which will published as a knowledge based article
5) the user can then inspect the hash on their own device to see that it hasn't changed
6) all of this can be audited by third parties
can you see that if this done in the cloud we have no transparency, we have no access to know what database is being used and how it is used or what is in it
basically apple is placing the database on a table and allowing the whole world to gather round the table and affirm that the database hasn't been changed or substituted (the phone) since all eyes are on it
all of this makes the process far more secure than doing scanning on the cloud where we have no idea how it is taking place
Regards Apple Control