Adding camera shortcut to lock screen lets you open the camera app and take instant shots without unlocking your device. On Samsung Galaxy S5 do as follows to add camera shortcut to lock screen:
1. Open Settings application
2. Go to Device tab and open "Lock Screen" settings
3. Under Swipe Options make sure to mark the "Camera Shortcut" option
4. Now go to lock screen and you should see the Camera shortcut on the bottom right of the screen.
5. Hold your finger on the camera icon and swipe in any direction until the Camera application is launched
** Note that, since you are bypassing the lock screen, some camera options like camera modes are disabled.