Hmm not sure what you mean. The hashes are shipped with iOS, and then (if parental controls are enabled) compared with the hashes computed against the unencrypted data on-device, and displays a warning to the user and their parents.

I'm not sure how the image is displayed on the parents' device - it could be sent from the child's device, or the image used to compute the hash that the child's image matched could be displayed.