If only round or oval shapes are needed, it would be easier and better to create them within Site Designer, and not having to use the help site mentioned on the page for the 'Shaped Images'.
All you do is take a rectangular image for the oval, a square one for round, and then you give them a border radius of 500px. Such things as a border or some drop shadow, which both have been used here, will look nice, but it is optional.
If you need to space them out a bit, don't use padding, that will break the design. Use margins instead.
And this one does work in IE11.