Sure

go to My Profile, then click Edit Avatar. It will show you the screen with all the animal avatars on it; scroll allllllllllllll the way to the bottom and there will be the option of using a custom avatar, you can either upload an image from your computer or use one from online. You can use many different file extensions (jpg, gif, etc, it gives you a list) and there are file and image sizes listed for each one.

HTH!