how can I make GIF over a static image?

[rich2005]

Nope, you have replaced the blues and greens with mostly white. That still has to be removed to give transparency for a new background to show.
Using a color-to-alpha and back to a semi-transparent dinosaur. Quite a big gif with the new back ground
https://filedn.com/lkb9dw6mEfXSsOu9uKLaM...imised.gif