Override Hyrax "create_derivatives" method to restrict "derivatives"/
thumbnail creation to safe file formats. Instead of trying to create
thumbnails for "everything and the kitchen sink", only create
thumbnails for file formats/MIME types that the the ImageMagick
developers consider "web-safe":
- GIF
- JPEG
- PNG

For details on what ImageMagick considers "web-safe", see here:
https://imagemagick.org/script/security-policy.php

Also, don't generate derivatives at all for non-image formats, because
those are even worse from a security standpoint. For example, audio and
video files would otherwise be fed into ffmpeg, and document/office
files would be fed into LibreOffice. Neither ffmpeg nor LibreOffice can
be considered anywhere near safe enough to read/parse/convert any files
inside a web application.