Image previews in nautilus

I wasn't getting previews for images on a compact flash drive attached via a USB connector in nautilus. Turns out, nautilus seems to believe that isn't a "local" drive, so under Preferences, Preview, Show Thumbnails, one has to drop down to "Always". Also see http://ubuntuforums.org/showthread.php?t=244898 for how to get around the error "The filename "..." indicates that this file is of type "jpg document". The contents of the file indicate that the file is of type "JPEG image""