Are there any video editing tutorials about overlaying animated smiley emoticons over faces?

I have a prank video I want to share, but want to hide the people's faces with animated emoticons.





Are there any tutorials that describe how to accomplish this? Tools to use doesn't matter as much as just the technique of how to accomplish this.|||I think a "overlay", and there is a filter effect named Pan in MPEG Video Wizard DVD can do things like that. All you have to do is to set the Start and End position of the person's move trajectory, then the picture will stays in place when the person moves. If you are not satisfied with the picture size, you can use another filter effect named Zoom to resize the picture.





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