In the early days of Android taking a screenshot on a phone or tablet was a pain, but now the ability to take a screenshot is built into the OS. For the vast majority of Android phones and tablets, to take a screenshot you simply press and hold the power and volume-down buttons together. After a few seconds the screen will flash and a notification will appear in the drop-down bar at the top of the screen, giving you options to delete, share or edit the image. You can also access the screenshot from your Gallery.
@Alexey.Rodionov
It's true that the procedure you are saying is workable from an end-user's perspective.
However, I'd like to see the possibility to save a screenshot/frame by code (from a developer's perspective)...