Stamperix,
Having stamps in my hand, I always succeed in establishing the direction of paper. And this goes for US stamps as well.
Judging scans is a different matter. First of all, you should cleanse your stamps so no remnants of hinges or dirt are there.
Your left hand stamp has a horizontal grain.
When scanning, take a high resolution 1200 dpi at least; take a 90 degrees turn and scan again! Make sure you have a lot of contrast!
Select an area of the stamp surface [of your scan] enlarge it and make a screen dump!


The grooves [the embedding of thicker fibers] are not always so clearly visible, but once you are used to it looking at it this way, it will be easy :)
Rein