I found the post below asking about putting an image in the background. It was closed after 14-days so I’m saying it again here. It would be a nice feature. I still think it’s not been implemented.
So if a Dev is watching, add my name to the list of people who’d like to see this feature, like @mati-nvidia did before.
It is already in USD Composer. It has been for a long while. Look for XR Composition if you just want to place a non-calculated background in your scene. If you are talking about a background image that is actually part of the rendered calculation then you would just add that image, ideally a 360 HDRI to a domelight