O_o As far as I know there isn't one. It resizes whatever you have to the right size. As far as file sizes go, I put up a ridiculously large animated one just to see if it could support it. It did!
Could just be a hosting problem. The size of each avatar is 60 x 56, but as OldManClayton said, any picture will be resized if too big. If it is a hosting problem, try http://imageshack.us
you have to host your avatar on an external host (unless you shamefully use a default) so file size is only limited to your external hosts upload size limit. actual height and width doesnt matter as said before tdc resizes your image to 60x56 pixels.
What was happening was that you were getting the link from your page instead of the direct link. That counts redirects and where the click came from and goes through stuff you don't need.
Well I just used the stormpages one and it still didn't work. I'll try it. Edit: Great. I got it to work, but it's waaay too small. No one can read it, so I guess I have to go with another anyways.
Edited by dndfreak
Vegeta? What does your mother say about my power level?