I suggest you just try running optipng on some random PNG files you have on your HDD. Results vary greatly, but I've seen savings between 10 and 20% on files co

I suggest you just try running optipng on some random PNG files you have on your HDD. Results vary greatly, but I've seen savings between 10 and 20% on files coming from GIMP where I always set the compression to 9 (maximum). I never touched Photoshop in my life so no idea what you can tune there and what its defaults are, but general experience shows that a lot of people either just don't bother and go with the defaults, or go all crazy clicking and manipulationg everything without knowng what's going on. I agree with you that for JPEG there is no silver bullet, but like that other comment here suggests, you could perfectly just run optipng on max settings in a cronjob and call it a day, because you know there will be absolutely no quality loss if you don't explicitly request it.