Beside of some bugfixes Virtual Mirror 0.5.2 can handle *.png files for the glasses frame with custom defined transparency. I have back-ported this functionality from my Adobe Flash Virtual Mirror to the HTML5 version right now. It works similar.
This release 0.5.2 can be tested here by passing goggles.jpg with white background and here by passing googles.png with a custom defined alpha channel to Virtual Mirror.