Can I ask again if it is possible to upload a gif avatar? I have seen a few users have one 
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.I don't think that's possible. Are you sure you've seen gif avatars? I haven't spotted one myself. I tend to find them pretty hard to take if there's a page full of them flashing away at you.
Theymos has said that he will not allow gifs, (for now) but will keep them for old members who have uploaded a gif in the past. (Before the forum was hacked.)
If you want to see a user with a gif avatar, there is one here:
https://bitcointalk.org/index.php?action=profile;u=24792