In a graphic novel, I think that body posture has to make up for a lot, considering less words are you to describe how a character feels. In the pane below, taken from League of Extraordinary Gentlemen, I believe the author tells the reader quite a bit about the character based on how their bodies are positioned.
For instance, in this strip, Quatermain and the invisible man both look quite relaxed. The author put them in comfortable chairs, possibly signifying that the two characters take life less seriously than others in the picture. Although we can’t see the invisible man (obviously) we can tell he is holding a cigarette and dressed in very comfortable clothing, including slippers. Perhaps this is coupled with his extremely nonchalant attitude toward morals to further his image of not-giving-a-crap.
Dr. Jekyll, on the other hand, looks extremely nervous, which lines up perfectly with what his dialogue reveals about his character. The way he is sitting all scrunched up makes it look like he doesn’t even want to be seen. He’s is also sitting in a very unforgiving looking wooden chair, in stark contrast with the pompous chair Quatermain is sitting in.
Wilhelmina looks like she is in charge, just like always. Her straight posture and focused glare give the impression of someone who wants to get something done, NOW. She is looking at maps, which may signify that she is the only one who actually is planning on working out what the group will do. The drawing of her also suggests she is comfortable sitting at Nemo’s head desk, where others might feel intimidated with the captain right behind them.
Speaking of the captain, His demeanor shows one main emotion: annoyance. From his use of the word fancy, to the fact he is standing right over Wilhelmina’s shoulder shows that he doesn’t like what is going on. He is holding a weapon in his left hand, possibly signifying that he doesn’t trust these people on his ship.
Just in this short analysis, I think it is clear how effective pictures can be at displaying emotions.