Boxes are really important in many kinds of presentation. In a zooming UI like Prezi they can be especially important as they help to group different sections together and reduce visual “clutter”. Grouping is a fundamental design principle!
But Prezi does not do well at these kinds of container - there are only 3 kinds of frames.
I know that I can create transparent gifs and upload them so they can be my visual containers, but this option is not adequate. Why? because they cannot be flexibly resized. If I create a rectangular box as a gif, it is locked in the dimensions I originally give it when I make the gif. If I decide to add more contents to my container, I need to make a new gif and upload it again. I cannot in Prezi play with the spacing of my content items and the width and height of my container to find what looks best.
So please give us more shapes or control over shapes (fill, no fill, color, line thickness, width, height). Right now I would kill for a rectangular frame that was not solid.
Alternatively, let us distort (change height not width) of images.