To speed up web browsing in particular viewing picture your web browser can store a picture it has downloaded once and store it in the cacche. When you go back to a previously viewed page windows by default sees if any of the images are in cache and will use them rather than down load them again and slowing your browsing. Problem is when an image changes on the server but you still have a copy in cache. Personally I use Opera its a lot faster than IE.....
For all you die hard IE users here is a quick cache how to.
You can configure basic caching parameters in Microsoft Internet Explorer (IE). To set cache parameters, click Tools, Internet Options on the IE toolbar. In the General tab’s Temporary Internet files section, click Settings. Possible cache settings in IE 5.0 and later include Every visit to the page, Every time you start Internet Explorer, Automatically, and Never—the most dangerous setting
Every visit to the page. When you return to a previously viewed page, IE determines whether content has changed since you last viewed the page. If the page has changed, IE displays the new page and stores it in the Temporary Internet Files folder. IE checks for changes once per session.
Every time you start Internet Explorer. When you return to a previously viewed page, IE determines whether content has changed since you last viewed the page. However, on subsequent visits to the same page, IE won’t check for new content until you restart the browser. To reread content from the server, you must manually refresh the page.
Automatically. When you return to a previously viewed page, IE won’t determine whether content has changed since you last viewed the page. Instead, IE checks for new content only when you return to a page that you viewed in an earlier session or on a previous day. Over time, if IE determines that images on the page are changing infrequently, IE will start checking for newer images and content less frequently. Again, to guarantee that you’re viewing the most up-to-date content, you must manually refresh the page
Never. When you return to previously viewed pages, IE never determines whether content has changed since you last viewed those pages. The Never option offers the fastest browsing performance but causes the most problems by ensuring that you don’t see page updates. To force the browser to display up-to-date content, you must click Refresh or delete all files from IE’s Temporary Internet files folder.