background image with nodes

I have and image file created with UV Image editor and a simple cube mesh object. I’ve followed instructions from several different tutorials but I can’t seem to get the cube to composite with my background.

I have in Node Editor/Compositing:
Render Layers Node/Image -> Mix/Image (Simple cube object with Glass BSDF material colored red)
Render Layers/Image -> Mix/Fac

Image Node/Image -> Mix (Simple blue 1920x1080 background generated from UV Image Editor)

Mix Node/Image -> Composite

Mix Node/Image -> Viewer

What I’ve tried:

  1. I thought it was a regressive bug so I tried 3 different versions of Blender on Windows and Linux.
  2. I tried Jonathan’s tutorial from 2013
  3. I tried the “How to composite in a background” tutorial at stackexchange.com.

I would appreciate any help you guys can give me. I just started using blender about 3 weeks ago so this could be a simple issue of me missing something simple.

First, does at least one of the images have a transparent background? If one of them has a transparent background, then in the compositor nodes, the node you’re looking for is the Alpha Over node. You want the background plugged into the top color socket and the transparent image plugged into the bottom socket.