bigger & animated pictures in signature

1) Why the picture's resolution size limit in our signature is too small?
Actually, the limit is 500x100 pixels. 500pix is good, but 100 is too small.
It should be like 200-250 vertical at least.

Why the moderators don't have a size limit, they're more important or what?

2) Why we can't insert animated picture in our signature?
It'll be very cool if we can.