You could check out the app called Ownskin.
I haven't tried it so I don't know what filetypes it'll take, or how it works.
If you're trying to use an animated gif you'd saved, and it only takes jpgs, for example, then you'd split the animated gif into separate pics, save each as a jpg and import them to the app.
(again, I haven't tried it so I'm not sure what is required).
HTH, would be interested in how it works out, if you try it.