This worked for me: I have a Photobucket account. For copying an image to a post from Photobucket you click on the "img" address, the 4th/bottom choice on the right side of the window with your proposed avatar displayed in it. But don�t do that. That did not work for the avatar, so I just tried them until one worked: second one down, "direct." Copied that and pasted it into the appropriate field in my profile. ('Specify avatar by URL'.)
I made my avatar in Photoshop Elements, sizing it to 383 pixels/side, which someone (Rocker?) said is the max size; saved that as a JPEG for uploading to Photobucket.
When I finally got the right address in the 'specify avatar' field I hit return and it was done. I just fumbled through all that again tonight, as my avatar mysteriously vanished after making an unrelated change in my profile--operator error, I have no doubt.
For what it's worth all this was done using a MacBook Pro.