IMHO, I don't believe that there would be any copyright issue here.

My reasoning is as follows:

If I use the term "Bruce Wayne" in a general conversation, that,
in itself, is not a CopyRight infringement. However, if I claimed
ownership of "Bruce Wayne", and used it as part of a marketing
or identifier for some product or service, obviously That would be
Illegal under CopyRight Laws.

So, The use of an Avatar in these forums is Not meant as a
means of Marketing or Advertising, but as a visual identifier of
who I am. Even though it is My Avatar, Here, I am Not
claiming "Ownership" of the actual image itself, just an informal
association.

So, to me, it seems like there is no copyright problem whatsoever.

However, what about the instances where a person advertises a
service or site for profit generation in a post or thread, who is
using an image for an Avatar that is copyrighted by somebody
other than him{her}-self? Would THAT be considered Legally
Actionable?

-Lou