There are a few ways how to do it -
- Firstly, try to Turn on the silent mode. If doesn't work, continue to second step.
- Mess with the Camera settings and try to find the sound settings. If still nothing, continue:
- If first two don't work, follow this step - it's a bit more difficult (and requires root) but it works.
- Download Tasker
- In profiles, create a new task.
- Select application - camera.
- Give it silence mode in audio options.