I just recently learned that Photos app has a quite a lot metadata for the images I have taken, try searching for "fruit", "book", "food", "baked", "bottle". As a feature this is pretty neat, it simplifies searching for past pictures much easier. In addition to this the logic can detect people from pictures and even identify them.
However I am concerned about the privacy factor. I have not enabled iCloud Photos sharing. Yet when I take new photo of an apple in Airplane mode, the search finds it as "fruit" only after I have enabled Internet access again. This means that Apple is sending my images (or some derivates of them) to their servers to be processed.
I haven't found any source that explain exactly what happens there, so I can only guess.
Does Apple really send photos to their servers or am I doing something wrong?