Ghost Caught on Film?

What is seen here in this close up of an empty sanctuary defies explanation.

The image was shot last summer at an old gothic revival church in Oklahoma City. The lighting was too dark for a proper shot of the transept, but the brightly lit sanctuary beyond prevented the flash from firing. This caused the camera to automatically adjust to a slower shutter speed, hence the motion blurring seen here. However, the remarkable thing was the sanctuary was completely vacant at the time.

 

Blown up, it has the appearance of a woman in a blue, short-sleeve blouse.  Upon interviewing church members, it was learned there was once a woman who fit this description at the church. She frequently sat in those pews until she died in the 1980s.  Subsequent exploration of the area, the image's EXIF data, and the camera could provide no explanations. No other photos emerged with this anomaly present (and one was taken a scant second later without said figure).

 

An on-location investigation was conducted that brought up some anomalies (pipe smoke in an area where someone who smoked a pipe could be found; the sound of a large group of people talking was heard in the sanctuary as coming from the fellowship hall in the basement, but an investigator in the hall heard nothing; furtive figures glimpsed in choir lofts, etc.)