This is actually referenced in the article. You can use the Last-Modified date and the server will either return a 304 (Not Modified) or the modified image if it is newer.
I read that, but if you say "this image won't change for exactly one year" and the client doesn't even request that resource from the server any more, how do you start that dialogue again?
pork has offered that you add a junk parameter to the end of a GET request and that should disrupt the cache, I'll need to read in to this. I'm interested in optimizing web speed as much as possible and this sort of thing and caching has always been something I've understood poorly.
Yep, that's the problem with long expiration dates -- the client may never check again (that's what we wanted, right?). The workaround is to request a new url which restarts the process.
Separately, the easiest way to get started with all these optimizations is to run the page speed check online:
I've actually been playing around with this stuff all day, pretty much since my last comment above. I've enabled smarter caching on my website, replaced multiple image requests with a single spritesheet, optimized my images, and cleaned up my CSS file to remove unused code. Google's PageSpeed has been an invaluable tool, as well as webpagetest.org which breaks down the data in an intelligent way.
Turns out Google Analytics is actually doubling my page load time, but the data is too valuable to give up.
