Also noticeable is the thicker line that looks to kind of be a part of the "O" that is kind of curving down the middle splitting the dragonfly with the albatross. It seems to turn the "O" into a yin-yang symbol. This symbol is the epitome of Taoist belief/philosophy and represents the importance of balance in life and nature.
Everything in reality has some sort of opposite to it, it is actually the fact that things have opposites that allow us to define and understand them. Would "hot" have any kind of meaning to us without the existence of "cold"? Of course not, and this fact shows us that both sides of the spectrum are needed in life and must be equally balanced. For example, since "good" cannot have meaning (or rather exist) without "evil", then it is not a good thing for "evil" to be wiped away. Even so, they must be equal in balance; however, there are so many things in the world of our existence that are of unequal balance, in which need to be rebalanced. It seems that the one who brought up earlier the dragonfly and albatross representing the smaller and larger respectively is definately on to something.
As you may notice, this yin-yang symbol is a little bit altered, or rather "unbalanced". The side of the albatross is too big; however, the side of the dragonfly is making pursuit in an attempt to make the balance equal again. You could probably correlate the duality of the smaller and larger with anything in life and nature, rich/poor, powerful/weak, peace/war, the list could go forever. The main idea here is that these two sides also generally represent qualities of masculinity and femininity, with the state of the world right now being in control by these masculine qualities. There is no balance in this world we live in currently, and since the dragonfly "naturally" flies northeast, it could as well show meaning in that balance is a part of our "natural" world.
It's funny how I had never really looked closely at the "O" symbol of Opeth, and now that I have seen an up close picture in a thread about symbolism I could point out all of this. For all we know maybe Mikael didn't even mean for it to have any type of meaning at all, and one day he sees this thread and is like "wow, I just came up with a neato lookin' symbol and accidentally stumbled upon all this!". Although, knowing Mikael, and thinking about the types of ideas throughout Opeth's music, I would highly doubt the symbolism is a mere coincidence.