Access Screenshots directory path for different devices programmtically

Question

I have requirement that whenever use capture screenshot from any external or internal app then user should notify that screenshot has been captured. For that i came to know that i can use FileObserver.

Okay, So i can do that. But my questions are:

1. How to access Screenshots folder for different devices?

Because some devices contain in DCIM folder and some devices with Pictures folder and for other devices actually i don't know.

2. Do I need to use FileObserver in activity class or should i use background service and put FileObserver in that service class?

Thank you in advance!