Here I'm going to explain how you can contour something in Gimp with the Path Tool to gain an exciting animated gif. You also can use a tablet and pen, it is just not what I'll show here. I thought people without a tablet should also be able to do this tutorial.
For following the tutorial you need to know how to make single images, which we have talked about earlyier in the Lesson about making a Gif from a movie.
Once you have imported the images do the following:
Choose Shift + the eye symbol of the bottom layer in the layer tab to make only this layer visible.
For the ball you can use the Ellipse Select Tool plus in the Edit menu Stroke Selection.
When you've finished the outline of your first image set the layer opacity back to 100%. The result should look something like this.