Update 6 change notes:

Reviewed all the terrain bonuses for all AGOT regiments. Changed most of them to better suit the areas they're recruited in.
Added one longbowmen regiment for the Blackwoods - recruited by the owner of the barony of Raventree Hall
Added one infantry regiment for the Brackens - recruited by the owner of the barony of Stone Hedge
Added 2 new regiments for the Riverlands, recruited by all of that culture: a heavy infantry regiment and a light cavalry regiment.
Added a new picture for Riverlands Bows, and used the old one for the new archer regiment of the Blackwoods.

Update 5:

Corrected some spelling errors.

Changed the name of some of the regiments in accordance to the lore. For example "The Knights of Winterfell" are now "The Sons of the North", to reflect that knighthood
was an exceptional custom in the North. It existed, but it was a rare occurance in the Northern Culture. Tanks to the points MarkKaluger made.

Changed the description for the Wavebreakers as a compromise, to represent that they're not Ironborn, as the use of cavalry was next to non-existent in the Iron Islands.
Thanks again to the arguments made by MarkKaluger. In the future I plan to change this in a more realistic way, and the Ironborn will probably not be able to recruit cavalry
from the start of the game.

Remade the image for the levies to a better quality one, thanks to SteelGod.
Remade the images for Winter Wolves and Wolfswood Rangers to better quality ones, thanks to SteelGod.

Corrected the missing text for the Dreadfort regiment, which made them unavailable in the previous version.

Added two more Vale regiments:

1. The Guardians of the Bloody Gates
2. Pikes of the Vale
Added a new image for the Hunters of the Moon.

Update 4 bring in some new units for these factions:

The North:
1. Winterfell Knights - heavy cavalry regiment recruited by the holder of Winterfell Castle
2. Winterfell Guards - heavy infantry regiment recruited by the holder of Winterfell Castle
3. The Dreadfort Impalers - elite spear regiment recruited by the holder of the Dreadfort.

Ironborn:
1. Harbingers - Ironborn archer regiment (cultural)
2. Kracken Guard - Ironborn pike regiment (cultural)
3. Wavebreakers - Ironborn "medium" cavalry similar, but a bit better than the Outriders (cultural, 80 men instead of 100)

Riverlands:
1. The Twins Guards - heavy infantry regiment recruited by the holder of The Twins Castle.

Various unit terrain bonuses and seasonal penalties and bonuses for most of the regiments.

Added images for the three Holy Order units, but the A.I. doesn't seem to be keep on recruiting them.
Changed the Barrow Knights image.

Version 2

Changed the Dorne images' background to better fit the area.
Changed the Camel Riders background.
Added levies and knights pictures for the 2 sections of the army UI.

Thanks to SteelGod for the input and ideas.