Picture fills may appear convincing or confusing depending upon the type of picture you use for the fill. Do remember that using a detailed or crowded picture as a fill for a small shape will get you no awards for slide design! It is best to use pictures that have one focused object or are subtle in nature for this purpose. Any shape on your slide in PowerPoint 2016 for Mac can be provided with a picture fill in the same way as you add or change solid fills or gradient fills.
Add picture fills to shapes in PowerPoint 2016 for Mac.