Hasn't been like that for years unless you're running a custom setup. The default is no privacy.

It’s done on device, for the most part.

Apple did explain the technology in a technical paper published on October 24, 2024, around the time that Enhanced Visual Search is believed to have debuted. A local machine-learning model analyzes photos to look for a "region of interest" that may depict a landmark. If the AI model finds a likely match, it calculates a vector embedding – an array of numbers – representing that portion of the image.

The device then uses homomorphic encryption to scramble the embedding in such a way that it can be run through carefully designed algorithms that produce an equally encrypted output. The goal here being that the encrypted data can be sent to a remote system to analyze without whoever is operating that system from knowing the contents of that data; they just have the ability to perform computations on it, the result of which remain encrypted. The input and output are end-to-end encrypted, and not decrypted during the mathematical operations, or so it's claimed.

The dimension and precision of the embedding is adjusted to reduce the high computational demands for this homomorphic encryption (presumably at the cost of labeling accuracy) "to meet the latency and cost requirements of large-scale production services." That is to say Apple wants to minimize its cloud compute cost and mobile device resource usage for this free feature.