The idea behind this tutorial is from http://pptheaven.mvps.org/, which is a great place to learn amazing thing about PowerPoint.
The trick behind this video is simple. First we put a full original size picture into the slide and then make it disappear. Then we apply Grow / Shrink effect and reduce the size of the picture to the size you want the picture to appear during slideshow e.g. 5% of the original size. Then we apply Appear effect and then apply Grow / Shrink effect up to 800%. So, the picture is actually zooming back to its original size while maintaining the picture quality.
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