Not documented so much as just... Known. I did a google search for my avatar too. Something along the lines of mad scientist, and this is what I got. It'll work for hanging onto the pic, but the quality's a good bit lower.
ROFL, I was going to get a Tepig avatar or something like that since it was my starter in my first purchased Pokémon game (seriously), but I ended up deciding not to get it and just didn't pick something else.
(I'm curious where this is documented now that you bring it up. )
NEway, I saw the Gen. VI announcement and loaded the starters, and Fennekin just stood out as a nice Pokémon, and a quick Google search led me to this image (bigger, something like 196x200). I wanted to hang on to that one, so this was my solution. Also promotes Gen. VI. :D
It's not for most people, but most people haven't been as active as you have, or they have gotten an avatar. I almost want to say that you're known for not having one by many of the junkies on this forum.