This plugin cannot optimize theme images. While I’d love to implement something like that (it’s been a common request), there are way too many variables to even attempt it. That said…
If you wrote your theme, it should be relatively trivial to do a one-time optimization of those images. There are many tools out there to do the job (but you’ll have to re-upload the images to your server), just goolge ‘image optimizer’. There are many online services, and also some programs that you can run on your own computer. I think there is one called ImageOptim for Macs if memory serves me correctly.
If you’re using a theme by someone else, you should ask them to optimize the images, so that an update doesn’t overwrite the optimized images.
I’ve used PNGGauntlet on Windows with good success – just ftp/scp the files down to your machine, optimize, then upload again, overwriting the existing. Check permissions on the files that you re-upload to make sure they didn’t get messed up.
Keep in mind that a theme update may push down unoptimized images – you’ll have to re-run the process if that is the case.
it’s in the latest dev version, although not finalized, it works
