I tried Squoosh
Damn effective in reducing the file size of an image, I must admit.
Then, to see if there was any phoning home during the process, I quit it, relaunched it, and cut my WiFi. It worked a charm. Of course, I still need the WiFi to call the page, but it does not seem to do anything network-wise once it's launched.
Biting the hand that feeds IT
