USPTO/Apple
A diagram included in the patent application.
$4 is titled "locking and unlocking a mobile device using facial recognition," and would let users unlock their devices by taking a photo of their face to prove who they are. It's a biometric alternative to Touch ID, Apple's fingerprint scanner.
Of course, facial recognition security isn't new - $4. And more recently, Jack Ma - founder of online retailer Alibaba - $4. The "Smile To Pay" will let users pay for goods using their device using facial recognition to authenticate their identity.
One interesting angle of Apple's patent is that it continues to secure your device even after it has been unlocked, however. A device with the technology enabled would continue to periodically take photos of the user: If the user no longer appears in the images, the iPhone will automatically lock, blocking unauthorised intruders from accessing the device's contents.
There's no guarantee Apple will implement the technology - the Cupertino company obtains numerous patents that it never uses. These can be precautionary, or intended to trip up or block competitors. $4, selfie-secured iPhones sounds surprisingly plausible.