the phone in your hand is a wide-angle lens held eight inches from your face. the mirror in your bathroom is not. this drags the focal length from "selfie camera" to "across-the-room mirror" and re-renders your photo along the way.
nothing leaves your browser. the photo is decoded and warped entirely on your device, in a <canvas>. it's never uploaded, stored, or sent anywhere — closing the tab deletes it.