The idea of duplicating an image, flipping one of them horizontally, and then combining the two has been around for a long time. So long, in fact, I had forgotten about it! Perhaps the problem is that it's me that has been around a long time.
Photos with leading lines are especially good for this. Depending one how you join the two images, you can get two different looks:
Perhaps even more interesting results can result from cropping the original first, and then duplicating it, flipping it and then joining the two halves.
I love the juxtaposition of the perfect symmetry of the background with the asymmetrical pose of my model Anne.
There are so many things to learn about post processing, as well as several different ways to accomplish the same task, that our challenge is simply remembering everything we have already learned!