Original 41.3% Smaller Use Lossless compression on theme and module images.
“Adding an Expires header to your components with a date in the future makes them cacheable, reducing the load time of your pages. Certainly this should be done with images, but that's fairly typical. Go a step further and add it to scripts and stylesheets, too. This won't affect performance the first time users hit your page, but on subsequent page views it could reduce response times by 50% or more.” http://stevesouders.com/hpws/rule-expires.php
What about caching and updating? So, you’ve updated an image or a sprite and you want that to download but your images are set to cache. Solution: Use a custom name for each update. For example append a character you increment or a date. Or, use a query string. This is what Google, Yahoo, and many others do.
Warning: While desktop browsers generally have large caches, mobile browsers typically have a cache only several MB in size.
Part 3: Mobile Devices
512MB The amount of RAM in the iPhone 4s and iPad 2. Mobile devices typically have 1GB or less of RAM. This helps extend battery life.
Let’s Get A Little Advanced
Alternatives To Caching If there isn’t much space to cache where else can we stick assets? Local Storage Google, Bing, and others put assets in local storage. Manifest Appcache Designed for html5 apps these can tell a browser to store assets for long periods.