MInecraft Animated Skins?

I have been on many servers where I have seen player's skins have lava or water running off of their backs or heads. How can I do this?

Ishtiak

They probably used an animated GIF for it.
it's basically an animated image, but a lot of stuff that requires pictures accepts it.

Drew

That's a server side mod and you can't see those skins on servers that don't have the mod.

Matthew