Some image formats support rotation settings. For example PDF
documents contain pages in landscape or portrait mode. If the pages
are in landscape mode the viewing application should rotate them by
90 degrees before displaying them.
This property reflects the angle (in degrees) by which the image
should be rotated before being displayed. This value may be
negative but should be a multiple of 90 degrees. ImageGlue defaults
to managing the rotation of images automatically. So in most
situations you will not need to test this property.