You can set the background image to an activity by setting android:background xml attributes as followings: (Here, for example, Take a LinearLayout for an activity and setting a background image for the layout(i.e. indirectly to an activity)).
Mobdro is 100% legal in USA. You donât need to worry about it. Up to now, there is no legal issues regarding Mobdro application. Mobdro streaming application is quite familiar to UK and US people.
There have been lawsuits over cracking software. It might be legal to use cracked software in certain circumstances. Educational resources for reverse engineering and software cracking are, however, legal and available in the form of Crackme programs.