How Google can check whether an application is installed from Play Store or Not? If a developer turns ON Google Play's Anti-Piracy setup, the application cannot access the play services if it is not installed from Play Store(so says Google). My question is how Google verifies this? More than that I need to know, if I can install an application from the play store, then modify the apk and then re-installs it in my phone manually(by enabling 'install from unknown sources') AND then use the play services?
i think following link can explain how google Play knows or in fact how any dev can know if a given app was installed from play store or side loaded:

How to know an application is installed from google play or side-load?