Re: HE MASHES CTRL+F5 LIKE A SUPR WIZCHARIRARD
I've explained this before, so I'll say it again, but slightly differently.
HTTP is a protocol (that's what the P stands for), the protocol includes a metric ton of communication 'commands' that comes along with requests to any web service. This meta data includes things such as LAST EDITED and the amount of data that ping takes is quite minimal, and you can send this "ping" for a webpage's meta data indefinitely until it suddenly changes, and then VOILA, you have the pic of the day.
Every time you use a web browser, it does all that pinging/meta data checking for you in a way that is mostly hidden to the end-user. Browser's will ask for meta data for a webpage and choose to load things from the cache rather than re-fulfilling the request with the web server if you already have the latest version.