Background images will only be displayed in
Camera Prespective view (Numpad 0)
Any of the Preset Orthographic views
Front/Back (Numpad 1 or CtrlNumpad 1)
Right /Left (Numpad 3 or CtrlNumpad 3)
Top/Bottom (Numpad 7 or CtrlNumpad 7)
Background images will not show in perspective view.
To switch between Perspective and Orthographic view use Numpad 5
Background images are used for reference only and will not be part of the final render.
Alternatives to background images are to use an empty as image or using a plane with the image mapped to it.
To use an empty as image use Add> Empty >Image
Select the image in the properties->Empty->Display tab
Alternatively, you can use the image as background for the world. Set the Texture coordinates to Window.