Small round dot, upper right corner of all...

If this dot is fuzzy, then you will need to have the camera sensor cleaned. If the dot is in focus, then you may have one or more dead pixels on your sensor.

You can purchase sensor cleaning kits at better camera stores and on line. Be prepared to spend 60 to 100 dollars for the kit.

You can also take the D80 into an authorized nikon repair center for cleaning or service.