PowerPoint Foregrounds

You frequently hear about PowerPoint backgrounds...but what about PowerPoint foregrounds?
Sure, text and graphics and such are all in the foreground. But what about using a .gif image with transparent "holes" in different shapes to reveal only what you want to reveal on your slide?
I offered a
circular foreground the other day for a circular Manadala experiment...but you can also create any number of foregrounds for your presentations....in any number of shapes, colors and sizes.
Simply insert the foreground you create over slides where you might want to reveal only a portion of your slide. Use .gif images with transparent "holes" to show only the areas you want to reveal.