HidCam for Android
When you tap "Start Service", the app will go to background and be hidden. Then you tap the TOP LEFT edge of your screen (can be changed to your liking) in order to take photo. All photos are saved on your SD card in /HidCam/ folder.
In order to turn it off, you need to start it again, and select "Stop Service".
If you need images to be hidden from Gallery, select "Hide Images".
Note: pictures won't be hidden when you switch to "Hidden". Only the newly taken photos will be hidden.
If you select "Auto focus", then image taking will be slower. If your device does not support Auto Focus, then this setting has no effect and will be automatically turned off.