When you pin a website to the Start screen on a WP8 you get a thumbnail of part of the page as it was at the time you pinned it. Later, on sites like Lifehacker and news sites they will move on and the image will no longer be current. This thumbnail is actually an image of the screen when you pinned it and it can be any part of the page, giving you some customization options.
Go to the page you want to pin and find an image on that page, a logo or some visual identity and enlarge it to occupy the top half of your phone's screen. Now pin it and you'll see that image on the tile. This is very cool. You read this here first.

See what I did with Lifehacker -