Apple tries to simulate the experience of "snapping" the camera when taking a photo on an iPhone or iPad using a sound similar to the shutter release on traditional cameras. But many users, like keyboard sounds, prefer a quiet experience.
As we read on Macworld, there is no need to turn the shooting sound on or off in the camera settings. So, if you don't want it not to sound when you take the photo, you have to use one of these three alternative techniques:
Attiva Live Photo: If you hear the shutter release when taking a photo, you don't have this feature activated, which captures some images before and after the moment you pressed the shutter, creating a mini movie.
If you hear the shutter close when you take the photo, you are not using the Live Photo feature on your iPhone or iPad. You also need to know that live photos take up more space than “non-live” photos, so if you have an iPhone with low storage capacity or take a lot of photos and videos, there may come a time when space is an issue.
To activate Live Photo you need to go to Settings> Camera> Keep settings> Live Photo.
Switch mute: With the Audio / Mute button set to mute (you have to see a small orange stripe to know it is mute), the shutter sound is not heard.
You can toggle the mute button on and off whenever you need it, although keep in mind that silence applies to all system sounds (except alarms and alarms), so you'll have a quieter iPhone when you “Mute”.
Turn the volume down to a minimum: You can set the volume of the warning sounds to zero.
Go to Settings> Sounds and Vibrations> Adjust with Buttons. If this option is enabled, you can use the Control Center or the volume buttons on the side to turn the volume down completely.
If the Adjust with Buttons switch is off, you'll need to move the Ringtones and Prompts dial all the way to the left for the same setting (sounds and vibrations).
Additional note: Some countries require devices to have a shutter sound when taking pictures. If you visit one of those countries (like Japan or South Korea) you will always hear the shutter sound. It appears to be SIM based, as those who visit those countries and insert a local SIM find that their preference for silent photos is ignored.