Note: It might be just a reflection. Perhaps there was glass or plastic between the photographer and the scene? You can see the large face of what I think is the photographer. The light upper right also seems to be a reflection. So the image of what appears to be an elderly man in (perhaps) period clothing and white shirt could be a reflection. But Erin says there was no one else around to reflect.
Even if it is a reflection, it does not rule out the possibility of a ghost. Many reseearchers believe that ghost images are more readily captured in reflective surfaces.
Erin responds: "I was standing outside the door taking the picture through the glass. I do have some that I am reflected in and you can tell it's me because I was wearing blue. So I'm positive the image on the stairs is not me. I also know that it was not anyone from the tour as it was hot, and everyone was wearing shorts and t-shirts. Plus, by the time I took that picture they had moved on to explore the garden."