Making animated backgrounds for stages...

[Alphatron]

I had been wondering about this for a while. You know how stages like Big Blue and Delfino have moving backgrounds? Or to simplify things, that one Sub space emissary stage where you fight Meta Ridley.

Now I have seen people make their own backgrounds from scratch for custom stages by using already existing pictures. And basically, I wanted to know if you could animate those backgrounds yourself. The main menu has an animated background too.