That looping JPG is all over the internet and is up for copying, don't accuse anyone of "Avatar thievery" unless the avatar was custom made, like mine.
Sure, but the idea to use it, especially with someone else using it, is likely taking it from them. Can't have multiple people using it at once or anything, get's confusing.
Actually, that reminds me: I actually found that someone stole my original account's avatar. :( And that one was custom made by another user for me, so I know it's mine... and the guy who made it, but meh, the point is he's using it when it was directed for me.