Why not store metadata, along with a checksum of the png, in myPublicPhoto.png.meow?

Labeling and metadata a separate concerns. "Edge detection maps" etc are implementation details of whatever you are doing with image data, and quite likely to be non-portable.

And non-removability / steganography of additional metadata is not a selling point at all?

So my thoughts are, this violates separation of concerns and seems badly thought-out.

It also mangles labeling, metadata and technicalities, and attempts to predict future requirements.

I don't understand potential utility.