Side by Side with Nodes?

I’m wondering if it is possible, and if so how, to within blender render an output like so:


The image on the left I would like to keep the same, and the one on the right I’d like to become my current rendered image. It looks like they are the same image but cross your eyes and concentrate on the middle one.

How is it possible to render to the right or left of an already existing image and push the whole thing out as the rendered image?