Spot the difference?
The pic was sent in by Tony Llewellyn.
Leave your guesses in the comments area below and I'll let you know the answer on Friday.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.