How to take a hidden photo?

Question

Android

The app should take photos on demand.
The problem is to take a photo - I call an activity (empty) and take a photo there.
The app pops up even if you make it hidden.
Another problem - if the phone is with a pin code, the camera crashes (
How to make a completely hidden photo?
Thank you very much!

Answer 1

The application can be left in the background and photographed on demand. Only now he takes pictures on the volume buttons.