Background Object

The background picture might be a landscape, into which your scene will fit. For this you assign a material, with the required texture in its color channel, to the Background object.

These images will be neither reflected by your scene's reflective objects nor lit in any way by the scene. Nor will they change with any change of camera settings. The background image will show through transparent and refractive objects but will not change with altered camera settings. You could compare it to a background layer generated by the Alpha Channel feature, on which the rendered image is then superimposed.

As soon as you have applied a texture to a Background object, it will be shown in the Viewport (taking the Offset and Length values in the Material tag into account). If this display distracts you, you can disable View Visibility off in the Basic tab. .
The background image will generally only be displayed in the editor view in which the Use as Render View option (View Menu) has been activated.
A CINEMA 4D object (the bridge) fits neatly into both a foreground and a background image (scene by Joachim Hoff).

Foreground and background pictures can also be tiled (see Tile).

Foreground and background pictures are scaled to the output format during rendering. Transparent sections of the background are ignored.

Animations and frame sequences can also be used for foreground and background pictures. In the case of a Background object, these sequences will also be displayed in the viewport.

TipBy default, only the top-most Foreground/Background object in the hierarchy will be rendered. If you want to change the Foreground/Background object during an animation, use the Stage object with a parameter track.