It’s not data harvesting if it works as claimed. The data is sent encrypted and not decrypted by the remote system performing the analysis.

From the link:

Put simply: You take a photo; your Mac or iThing locally outlines what it thinks is a landmark or place of interest in the snap; it homomorphically encrypts a representation of that portion of the image in a way that can be analyzed without being decrypted; it sends the encrypted data to a remote server to do that analysis, so that the landmark can be identified from a big database of places; and it receives the suggested location again in encrypted form that it alone can decipher.

If it all works as claimed, and there are no side-channels or other leaks, Apple can’t see what’s in your photos, neither the image data nor the looked-up label.