The Media Settings controls how your media is displayed.
You can change these settings at any time by going to Settings > Media, make your desired changes and then click Save Changes.
Your blog automatically resizes your images to three different sizes: thumbnail; medium and large. Most people keep these as per the default settings.
By default, enable image optimization is selected on all newly created blogs to automatically resize images when they are uploaded to your blog. This helps reduce your storage space usage and ensures that the images are optimized for viewing online.
The image optimizer works by converting png to jpg, resized and compressed; jpg are just resized and compressed. Maximum width is 1920 pixels by maximum height of 1920 pixels.