Just a personal note before we begin: I think most animated avatars are not a good idea. Just because you can doesn’t mean you should
How to do it
Officially, Twitter does NOT support animated avatars. If you try to upload one it may or may not succeed. Some people are successful only after many attempts on different days.
But it’s easy to do: simply find or create an animated GIF and then upload the image file as your avatar. Remember to clear cache afterwards (see http://bit.ly/QuickTwitterFix ) to make sure you can see if it worked.
Once you have an animated GIF, you can also use it for your background. If you use a very large animation, or if you set your background to tile, you may want to make your sidebar transparent (here’s how) so the animation shows through.
Options for making an animation
If you’d like to use an online service to make your own animation, try some of these websites.
If you’d like to search the web for an existing animation, try adding keywords to this search for animated GIFs.
If you’d like to create one yourself from a video using Photoshop CS5, try this technique: