Image Caching

[netfrugal]

Does anyone know a good explicit site that details how to cache images to the browser? This is for background images on sites, which are larger than normal. They are for the wallpaper effect.
My understanding is that browsers cache images automatically, but I would hate to keep reloading/downloading the same large image each time the browser refreshes.

-thanks!!

[NogDog]

One kludgy way would be to simply generate a random ID as part of the image's URL:

<div style='background-image:url(/images/background.jpg?id=<?php echo uniqid('x'); ?>)'>

[HalfaBee]

You can use .htaccess to send headers to try and force the browser to cache.

<FilesMatch "background.(flv|gif|jpg|jpeg|png|ico|swf)$">
Header set Cache-Control "max-age=2592000"
</FilesMatch>