Ok, maybe I had to logout first. As soon as I uploaded my avatar as admin, in my profile was displayed the default avatar for image approval (the one with the little clock at image corner).
So I supposed that I had to approve it, but in CB workflow module no pending action was displayed.
After working on it (I don't know why and how...) The approval avatar disappeared and my image finally was displayed.
Now if I change avatar, it's soon displayed and no approval default avatar is displayed first.