Have you considered simply sanding the underside of the cover down until it’s thin enough? I’d tape it down to a board with double sided tape, then you should be able to use an electric sander on it (if you don’t fancy doing it all by hand).

As for the thumbnail orientations, some photo editors don’t write the rotation instructions in a way that is correctly interpreted by other display utilities. Try rotating the pics in another editor and see if that works.