And I'm trying to figure out why this apparently feels so wrong and creepy to so many commenters here. I don't feel any of that. As far as I'm concerned, it feels... totally normal. Maybe I'm wired wrong or something, but I really don't see anything weird or creepy about learning from publicly available datasets (AKA observing your surroundings?). Nor do I see anything wrong in leveraging computational infrastructure to learn more from those datasets.
The way I see it - a hypothetical "creep" who takes a photo of someone and matches it with their public social media profile is fine. Where I draw the line is them attempting to put that into action through stalking, harassment, etc. because it hurts the other party. Trying to break into data sources that are not meant for public is of course a violation of personal privacy, which is wrong. Also, I consider a person with obsessive interest in another to have a problem that probably requires medical attention.
Are people so afraid today that the fact that another person notices them makes them uneasy?