GIF.
75X75
GO.
RESIZE FLASHY PICTURE TO 75X75
USE AS PICTURE UNDER YOUR NAME
You either animate a 75 by 75 avatar and save it as a GIF, or you find an animated GIF off the internet that is 75 by 75.
Ugh, why are people saying to make it exactly 75x75?
Please, keep it 75 by 75 or below, and follow the original image's aspect ratio.
What am I talking about?
Take a look.
Here is a PERFECTLY EVEN square.

It is on a 200x100 image.
What happens when you make it 75x75?

It becomes a loving rectangle.
What happens when you make it 75x38?

Look! It looks like it's supposed to!