Most of my users upload images in baseline format. If uploaded images are processed through a cron job once everyday using a jpegtran we can improve the performance of the site.This would benefit not just loading speeds we could also use such an option to brand images.
WHAT TOOLS DOES SMUSH.IT USE TO SMUSH IMAGES?
We have found many good tools for reducing image size. Often times these tools are specific to particular image formats and work much better in certain circumstances than others. To "smush" really means to try many different image reduction algorithms and figure out which one gives the best result.
These are the algorithms currently in use:
ImageMagick: to identify the image type and to convert GIF files to PNG files.
pngcrush: to strip unneeded chunks from PNGs. We are also experimenting with other PNG reduction tools such as pngout, optipng, pngrewrite. Hopefully these tools will provide improved optimization of PNG files.
jpegtran: to strip all metadata from JPEGs (currently disabled) and try progressive JPEGs.
gifsicle: to optimize GIF animations by stripping repeating pixels in different frames.
Not to sound pushy, but you should give it another shot and play with the config, then let it run for a few weeks. If you don't use settings that use a lot of extra CPU on each request then the initial CPU overhead is only high as it builds the initial cache. After that it's pretty much serving pages out of the cache and it stops processing things on each request.