Generating and using non-square thumbnails

I am developing a digital archive that will consist mainly of scanned documents presented as PDFs. Omeka cleverly generates thumbnails of the PDF and the cover image files, but they are square - and the documents are mainly A4.

The trouble is, I can't find any way to get thumbnails that are in the correction proportions. Is this possible?

Where you do this depends on what pages you are trying to change, but in general, just find any references to square_thumbnail in your theme and change them to thumbnail. That will make Omeka generate proportional thumbnails instead of cropped squares.

Doing so for exhibits requires a plug-in--you can see an example with the nal-document-gallery layout here: