I've been using PngOptimizer a bit lately and like pnggauntlet it optimizes png's to a lossless format while cleansing out bad/unneeded data.
http://psydk.org/PngOptimizer.phpSince this program doesn't handle jpg files, I use jstrip first, then convert them to png with pnggauntlet & finally use pngoptimizer on them. I find pngoptimizer to be much faster than pnggauntlet.
I've grabbed roughly 25,527 files, mostly images from this site using softbytelabs blackwidow to test these tools on.
Right now the images are using a total of 8.37 GB (8,990,199,585 bytes). I'll post back the results of optimizing them all with the above tools.
After clearing out some trash files (blackwidow made a bunch of copies of index pages) and running the tools on some files in the atlas folder, it's now at:
21,593 files
6.53 GB (7,021,207,557 bytes)
Even still I'm nowhere close to being finished yet especially with the super large maps in the PC folder... one is over 70 MB!