I'm using a very simple Refinery CMS application. Some of the images return a mime_type of application/octet-stream. These images have filenames which include an extension:
guid: 2016/03/03/31rcxe434_IMG_0844.JPG image_name: IMG_0844.JPG
guid: 2016/03/03/6hkn0yuiyx_GITW1.jpg image_name: GITW1.jpg
A Refinery::Image has an image_mime_type field, which is null for all images in this db, including images which return a correct mime_types.
It looks as the images table had an image_ext field originally, but that was removed about 5 years ago.