How can I use an image as background?

I must me daft, because it should be (and probably is) a simple thing, but I don't seem to be able to figure out where and how I can select an image to be the background for my pages/scenes?

How/where do I need to look in order to accomplish this?

There's a basic method ( Modify the Background Color or Background Image of your Document ) and a programmatic method you can use: Setting a background image for my project - #2 by MarkHunte

But you could also just drag an image into your scene and move it to the back of your element order to have it be your background.