I’ve updated this post with some extra advice about sharing images and videos…using Jing and posting to Screencast.com.
Jing is free and integrates fully with Screencast, to the extent you sign up for Screencast as part of the Jing install process. It’s the quickest way I’ve found so far to share images without having to resize.
Just take a screen capture of your design in Polyboard, capture with Jing, and share via Screencast.com. When you install Jing, a short tutorial pops up that shows exactly how to do it.