This page is meant for those who have server access. If you don't have server access, just use the TinyPNG integration by entering an API key to the Image Optimizer settings page.
To run the optimizers locally, install at least one of the image optimizers on your server, see instructions below. I recommend installing all optimizers.
Also, make sure your PHP installation allows the functions 'proc_open' and 'proc_close'. You can ask your host, or check the php.ini file, or create a PHP file with '<?php phpinfo();'.
Optimizers on Ubuntu:
Optimizers on CentOS:
Optimizers on macOS (using Homebrew):