I've been exporting Poser scenes to Blender for rendering (and fine-tuning, as you do) and did this scene:

...where the sky and hills are an image on a panorama prop. But the lighting was wrong: the setting sun didn't look like it was really setting.

The fix was this: adding a emission node, which then produced this. Shader available upon request. :)

Very nice render well done with the lights

Really great looking scene like the sort of early evening look to it

Wow that does look really good. Nice trick.

Instead of using an image plane with emission, it's also possible to have an image as the world background. I may have to show the alternate method's shader node setup, as it's not the most intuitive thing at first. (Would get warped oddly with the default texture space, and some other things too.) Thing about the world lighting is that it comes in from "infinite space", so it may effect the scene a little differently.

There you go. As for the red arrow? Just showing what you have to click for world settings rather than object in the compositor. (But I think most would know that by now.)