[simondotau]

The data is not sent to a "police group", it is sent to NCMEC.

From Apple's FAQ:

Will CSAM detection in iCloud Photos falsely flag innocent people to law enforcement?

No. The system is designed to be very accurate, and the likelihood that the system would incorrectly flag any given account is less than one in one trillion per year. In addition, any time an account is flagged by the system, Apple conducts human review before making a report to NCMEC. As a result, system errors or attacks will not result in innocent people being reported to NCMEC.

[douglasisshiny]

NCMEC then makes those images available to the appropriate law enforcement agency after the fact.

[simondotau]

Yes, if they're CSAM.