PRIVACY: How Pizza Night Can Cost More in Data Than Dollars. “Even a low-key evening at home can mean handing over a trove of personal information to high-tech companies.”

Sally and Kristen haven’t hung out in forever, so Sally suggests taking a selfie.

After Sally uploads the photo to Facebook, the app suggests she tag Kristen based on its facial-recognition system, which Kristen has given permission to use.

Facebook could collect Sally’s location based on the IP address used to upload the photo, which it could use to suggest local events that might interest her or show her ads targeted at people near a specific place. Its system also analyzes the photo as it does with all images to make sure there’s no inappropriate content.

The rest of the unsettling details are behind the WSJ paywall, but you might find a backdoor here.