Whats the easiest way to create screehshots of ios and android app for appstore submission

[pearlquest]

What is the best/easiest way to make screenshots of the app that follows the appstore guidelines?

[Michael]

1. Add a button with the following action (the image is saved to the documents folder):
   
2. Select the required device:
   
3. Set zoom to 100%
   
4. Click the button to save screenshot