Page Cache Control
Your web browser caches web pages you look at including its images.
A copy of the page and it's images are kept somewhere on your computer, depending on your web browser. This can be controlled with a <META> tag. It can tell your browser when to delete these files or whether or not to store them in the first place.
To tell a web browser when to delete cached content, use this tag in the <HEAD> area:
<META HTTP-EQUIV="expires" CONTENT="Wed, 26 Feb 1997 08:21:57 GMT">
To tell a web browser not to cache a page at all, use this tag in the <HEAD> area:
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Cache-Control" CONTENT="no-cache">