class="thumbnail" how to create a thumbnail of an html page

i want to create a thumbnail pic like what chrome browser does in representing most visited sites but i have no idea but when i inspect one of them i found 开发者_如何学Pythonclass="thumbnail". any idea ;because i have no idea about it are they using scripts or it is just a css or plug in ! and for that i am sorry i have no code .could you please help me or offer me some examples. note: the html page could include video pictures text map..etc

Chrome uses a background (although it should be foreground as it is content) image (which is generated internally by the browser).

You'll need to use something like webkit2png (running on your server) if you want to generate an image.