Sometimes you need to take a quick photo and you do not have time to unlock the phone, so this feature will be very helpful. It is nothing new, but it is unknown to many users.
To take a picture from the lock screen on your Note 8 you should simply press the power button on the right side of the phone twice. This will activate the camera even with the smartphone locked. You can also use the Bixby button in case you have enabled it for this function.