The process has been there for years. It used to be responsible for huge CPU spikes, but with newer processors it is less noticeable.
Yes, it is sending a hash and may be related to the announced, and then suspended, CSAM program. https://futurism.com/apple-scan-iphone-images-child-sexual-abuse
I fail to understand how this connection is needed for local facial recognition and indexing.
It is unfortunate that our machines aren’t ours with full control and documentation over OS processes. But much of this one is ten years old (back to when it was called photo…)