Here is what i tried and it worked. Please note i am using K3 note upgraded to Marshmallow -
Turn on your camera --> Go to Settings --> Click on the 3 dots to pull up further options --> Set Snap Sound OFF.
while using your camera just turn on the DND option and the shutter sound will be silent.
Hi there guys. Try checking camera settings if there's an option to disable it. If none, try putting your phone in silent mode.