Creating a mirror image is simple depending on what you want to do.
1) Assuming you're going to use windows, use a video driver that supports this. I think both ATI and nVidia have this option but am not sure. I know they offer rotate, but not sure about flip (mirroring)
2) Tell your emulation software to flip the image in one direction creating a mirror. I believe Mame can do this, but not sure about the rest. Check their docs.
3) If you're going to use real arcade boards or don't want to deal with software, all you have to do is swap either the vertical pair of yoke wires or horizontal pair (then rotate the monitor accordingly) and you'll have the mirror image you want. See BobRoberts web page about yoke flipping for technical info.
That said, playing most games in the mirror setup might be annoying, especially if you plan on leaving the reflected moon in the picture, but that's your call.