Lead Developer
GP doesn’t create image sizes unless you create them in “Customize > Blog > Post Images” and click the “Set image sizes” button.
WordPress creates multiple images when you upload based on the settings you choose in “Settings > Media”.
That being said, the pagespeed score doesn’t see all of the images created, it just sees the one used on the page itself.
A plugin like WP Smush is good, or running your images (that will show up on the site) through something like this helps as well: http://optimizilla.com/
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development