Okay, I guess the first trick is, I did the pie chart first, which looked something like this:
Then I saved that image, and uploaded it, so I could use the Add Image function to put a circular image over it.
Then the second trick is, I used www.lunapic.com which is a site that lets you do different things to images (and they have a Crop Image option with a circle shape). I used that function to make a circle crop of van Gogh's "The Starry Night" painting, that I then used to add to the pie chart image (above).
