My program is working with fax documents stored as separate bitmaps
I wonder if there is a way to detect automatically page orientation (vertical or horizontal) to show image preview for user in right order (meant rotate if neccesary)

Any advices much appreciated!

EDIT: Clarification:
When Faxmachine receives multi-page document it saves each page as separate TIFF file.
My app has built-in viewer displaying those files. All files are scaled to A4 format and saved in TIFF (so there is no change to detect orientation by height/width parameters)
My viewer displays images in portrait mode by default

What I'd like to do is automagically detect situation when org document was printed in landscape mode (eg wide Excel tables) then I'd like to show rotated preview for end user to speed up preview process

Obviously there are 4 possible fax orientation portrait / landscape x 2 kind of rotations.

I'm even interested simplified solution detecting when org doc was landscape or portrait (I've noticed most of landscape docs needs to be rotated clockwise)