An image with a transparent background is like a painting on a window: you can see all sorts of exciting things behind it, but you can’t reach through to touch them. αlphaPun.ch changes that!
αlphaPun.ch will trace the opaque part of your png or gif image. It will then punch through the alpha channel (i.e. the transparent bit), so you can click on things behind it.
What a truly useful plugin. Check it out. This will make your life so much easier.