Getting website thumbnails in a webkit extension

I'm wonde开发者_StackOverflowring if the WebKit browsers (Safari and/or Chrome) provide a method to generate or retrieve existing thumbnails for websites. If not, is there any way to generate these client-side? If even that is not possible, is there software or a particular API to generate thumbnails server-side?

Thanks!

To people from the future:

At the time of writing, this feature is only available in Safari 5.0+. You can get thumbnails from the Tabs API. Chrome doesn't have any similar features as far as I could find.