Is there any way i can insert an image that will serve as a background without losing its quality?

[TIMAI2]

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Background picture lock ratio

Hello to all I have background image and few objects on it (hiden buttons, textboxes,..). I want that the background picture is on every phone in its original ratio (not stretch like it is now). If on the picture is circle I want that user see circle not elipse. How to lock background ratio?