Can the sound of a picture being taken be turned off?
Camera shutter sound
Provided you don't have firmware from certain countries which require it by law, I believe you can if you go to Menu > Tools > Settings > General > Personalisation > Tones, and turn Warning Tones off. That will, of course, disable all warning tones.
or try the freeware "cCam" which disables the flash and the sound
Or just switch the phone to the silent profile, then switch back after.