This is a half rant / feature request…
The page for adding a background in SketchUp is just about the most useless this page could possibly be.
Adding a background to your model
SketchUp allows you add image files to your model and position those images such that they act as a background. For example, you can have a single image placed vertically behind a house so that you can study what will be seen from certain angles within the house.
Really… We can’t get more content on that page? Like how to do said task?
That writeup is a tad thin, isn’t it?
Well, it’s clear that you would like a more detailed discussion about this in the “Knowledge Base,” but it’s less clear whether you are also asking for more information here and now about this background feature.
Although you can simply prop up an image as a backdrop to a scene just about anywhere, SU has a far more sophisticated method: using a style with a watermark. The watermark is an image, which you can place in front of or behind the model. There are several choices for position–one of the corners or stretched to fill the screen.
Parameters for specifying an image file and the other options I just mentioned are on the Watermak tab of the Styles dialog (Window > Styles > Edit > Watermark settings (fourth tab).
-Gully
The description seems to be referring to to the import | jpg | as new matched photo option; this sets up a scene where the perspective and scale of the model can be manipulated to match a photo.
But it could also refer to placing an image on a plane within the model. (or multiple images to create a panorama)
(The watermark option is one possible solution, but the image used will remain overlayed/underlayed, no matter what angle or perspective you are viewing the model at.)
Whether the watermark overlays or sits behind the foreground subject is one of the options offered in the Watermark Style settings.
-Gully