When you look at the selfie screen on your smartphone it does NOT show you the same image that someone looking at their screen on their smartphone will see when taking the exact same picture of you, but not as a selfie.
Furthermore, the picture you take will look like the one on their screen, not the one shown on your selfie screen.
What’s the difference and why not?
A photo takes a true image of you (adjusted for light filters, red eye etc.) The image is not inverted as it is in a mirror. The image you see through a viewfinder, or on your screen when taking a normal smartphone picture is pretty much the same as the end photo.
The image you see when in selfie mode is an inverted / reflected image, that is, the image you might see in a mirror. If you have a mole on your left cheek, it will appear on your right cheek in the reflected mirror image when in selfie mode.
Probably worth spending a moment to consider what mirrors actually do, since many people aren’t entirely clear on this either.
Plane mirrors do not actually invert left to right. A mirror does not distinguish between up down and left right. You actually see a 180 degree rotation (that person is facing you) plus a left right inversion.
A better mental model might be to consider that the mirror is converting front to back, resulting in a perception of the image that you choose to see as inverted left to right.
Consider this little experiment, which you may enjoy actually performing. Lie down and look at a mirrored ceiling (if you can find one). You will say it inverts left to right. Now rotate 90 degrees while still facing the mirror. You will still say it is inverting left to right rather than up to down. Now get another person to lie down with their feet touching yours but orientated at 90 degrees to you. Your partner says the image is inverted left right with respect to him but you say it is inverted left to right with respect to you. Either this is a magic mirror or both of you are refusing to see it as a front to back inversion.
You look in the mirror and you don't see a left right inversion. You actually see a 180 degree rotation (that person is facing you) plus a left right inversion.
Unfortunately, although it may be both simpler and more accurate to see it as a front to back inversion, this isn’t the way it is generally taught.
We are not consciously aware of the world as it is, we interpret all our sensory inputs through the filters of mental models. Unfortunately we aren’t particularly good at building these models, so they are often flawed, and sometimes just plain wrong. There are many reasons for this, and bad teaching is just one of them.
Regardless, we prefer technology that is “simple”, “user friendly”, “easy to use”, and “intuitive”. Studies have found that these phrases do NOT mean what they say. They actually mean “it works like something with which I’m already familiar.” See also the Querty keyboard.
People who are used to the Apple / iPhone way of doing things have views on what’s “simple” and “user friendly” that’s sometimes very different from those of people used to Galaxy, Google, Amazon, Facebook, Microsoft, and so forth.
Apparently though, we have all gotten used to mirrors, and the mirror images they present, even if our mental models of exactly what a mirror image presents is somewhat flawed. Mirrors are disorienting when first used by young people, but then we learn how to use them.
Because we have been taught by experience to understand a mirror image, we expect to see things that way. Selfie cameras in phones are inverted to mimic mirrors. Reversing cameras in cars are also inverted to mimic mirrors.
If you are presented with a mirror that provides a 180 degree rotation rather than a front to back inversion, you have to re-learn how to use it. That's why phone makers chose to invert the screen in selfie mode. Otherwise people found it “non-intuitive” and “not user friendly”. We would have to re-learn how to use a non-mirror image. So they chose to imitate a plane mirror instead.
Hope these thoughts help.
PS - Here’s an outlier thought. If Vampires don’t reflect in mirrors, does this mean they can’t take selfies of themselves either? And do they use the flash feature?