It’s different from the camera’s physical sensor-cleaning system.

A Dust Off Reference Photo does not remove dust from the sensor. Instead, you photograph a plain, featureless subject such as a white wall, blank paper, or an overcast sky. Nikon software such as Capture NX2 can use that reference image to detect the locations of dust spots, which usually appear as dark marks.

The software can then use that dust map to automatically retouch or reduce those spots in later photos.

So in short:

• sensor cleaning = tries to shake dust off the sensor
• dust off reference photo = helps software identify and correct dust spots afterward

It’s a post-processing aid, not a cleaning method.