Comment 1 for bug 688144

Here's a single page from that book:

http://www.archive.org/stream/recueildevuesdes00ponc#page/n7/mode/1up

and the image that BookReader extracts for that page:

http://ia700103.us.archive.org/BookReader/BookReaderImages.php?zip=/2/items/recueildevuesdes00ponc/recueildevuesdes00ponc_jp2.tar&file=recueildevuesdes00ponc_jp2/recueildevuesdes00ponc_0007.jp2&scale=9.147180192572215&rotate=0

You can see the image itself actually includes a substantial margin above and below the book, all of which is cropped out in the BookReader display, although the left margin remains. It looks almost as though the image size is calculated for the full window, and then the top and bottom navigation bars are placed over it, covering the top and bottom of the image, instead of calculating the image size for the space that will remain between the nav bars.