2. Annoying mass texting aunt posts it to her public Instagram
3. Creepy guy takes a screenshot
4. Creepy guy posts it to Creepy Guy forum
5. FBI scrapes the Creepy Guy forum and the pic is uploaded to NCMIC database
6. Photo is hashed by microsoft's PhotoDNA and other software and shared out.
7. Apple matches the hash and flags the 17 family members accounts as all containing the image
8. Some non family member at Apple (probably a contractor) looks at your close family photos of your unclothed niece and nephew to determine if it's inappropriate, but since it meets the "large group" 15+ member threshold it is marked as "likely" part of a child photo ring.
9. All the accounts are now flagged as "potentially in violation of CSAM content"
10. Your account is disabled until "pending review"
11. FBI has enough evidence to submit a letter to apple and all other of the normal boiler plate companies for all subscriber data
12. You are now in the FBI database as a child photo suspect.
Testing can show the presense of bugs, but not their absence. -- Dijkstra