Okay, here's the deal. I thought I'd take a picture of my shooting buddy, Kathleen, as she carried her tripod, camera and camera bag up the stairs. It was totally unplanned, and I asked her to stop for a moment. I thought it might be a good portrait. It wasn't.
I shot five pictures for a possible HDR, but botched the exposure (too dark). I looked at it at the time and figured it wasn't anything to write home about, so I moved on.
I've been doing a lot of post-processing from older images lately, and looked at this one again. Then the ghost idea occurred to me. However, for that to work, I'd also need an image of the scene without Kathleen, so I could mask one and combine them. But I didn't have one. So, yesterday, I bit the bullet and decided to do it all manually.
I did the HDR processing on the five images I had with Photomatix, then made a duplicate image layer and set about removing her from it. I cloned some things in and painted a lot more in until she was gone. Then I reduced the opacity so she'd look more like a ghost, performed some more magic (like another round of HDR toning in Photoshop), and wound up with this image, which I'll probably continue to tweak for a while longer.
All in all, I'm pretty satisfied with the result so far.
Here's the original shot: