There used to be a service - IIRC called "please rob me" - that tracked users' movements based on geotags in EXIF data posted to social media. Pretty scary, and actually implemented. Most sites weren't stripping EXIF data at the time, so if somebody posted a photo 5min ago you could get latitude/longitude by just examining the file. If the coords wasn't the person's home address, you'd know they were away and open to being robbed.