I had a hard time understanding custom display objects, and figured it would be easiest if we had an implementation of the Image class, but as a fully custom DisplayObject. The polygon class available at https://gist.github.com/PrimaryFeather/2352107 is nice, but I found it hard to separate the polygon logic from the regular quad/image logic, which unfortunately is buried in QuadBatch, RenderSupport, and a few other places. So, I pulled out the rendering code from QuadBatch, modified it for the case of one single image, and added it to the CustomImage class.
Please note this is NOT intended for production code, as it's not batchable and would be highly inefficient. I only created it as an educational exercise, and a stepping-stone on the way to behavior that I need for a current project. Thought I'd share it with the community in case it helps anyone else.
The only problem is it's for Starling 1.x, I would've done it for Starling 2.0 but the project I needed it for is still on Starling 1.x