Superhuman, the $30-a-month invite-only email app is in the crosshairs of scandal for secretly allowing users to track when, where, and who has opened an email, even if they’re a stranger. But even if the app seems egregious, the idea is nothing new: It’s called a tracking pixel, and it’s been used for years to see whether you’ve opened an email. Here’s everything you need to know about tracking pixels, AKA web beacons, AKA pixel tags.
