atla-annotated:

Ozai’s portrait

Ozai’s hands are shown in a double abhaya mudra.The abhaya mudra is a
“Gesture of Fearlessness” or “Blessing”. Which, I guess, form Ozai’s point of view makes a twisted kind of sense. He is blessing the world with the progress of industrialization, and later with fire …

Ozai is standing on a lotus. The lotus flower does symbolize enlightenment in Buddhist teachings. Does that mean Ozai is supposed to be enlightened? Well, if you look closer you can see that his lotus is rooted in black flames and is covered in flames itself. If there is any enlightenment to be had it is through fire. Quite literally, if we take the finale into account.

Each Fire Lord’s portrait depicts their achievements during their reign. Sozin has the comet and his legacy (the history scroll), Ozai the cogs and furnaces of industrialization, as well as more flames than anyone else. Interesting, though, is that he is not depicted with the comet, even though it occurs during his reign and he plans to use it to conquer/destroy the world. 

Image source: One

More: The Handbook of Tibetan Buddhist Symbols