This app was mentioned in 2 comments, with an average of -1.50 upvotes
After trying out few applications I have found a decent one called High Quality silent camera by duaoddl. Takes photos without the shutter sound. However, the quality is not as great as stock camera's but the best amongst free silent cameras. There are also advertisements (not as much as Silent Camera does) and deleting is a bit slow. Otherwise pretty good one, or at least fulfills my requirements. Silent Camera was a good candidate as well but it had too much advertisements, especially those pop-up ones that makes sound (pretty much ruins the idea of having a silent camera). And Silent Camera's quality was also worse than duaoddl's silent camera. I couldn't save photos to external sd card on either even though it is said being supported.
use another camera app, like this one
https://play.google.com/store/apps/details?id=com.oss.mcam&hl=nl
[edit: downvote all you want, but it's still a great app for discrete pics.
I regret nothing!
hehehe