Image Optimizer can compress product, collection, and asset folder images.
Any images stored in the Settings > Files area of the Shopify Admin cannot be compressed or even accessed. This is because Shopify does not allow access for apps to this area so it is impossible for us to compress them. If Shopify opens this access up, we will add that functionality to our app. This includes homepage slides/banners, blog images, images in product descriptions, and images in pages.
If you have any questions, feel free to send an email. We are here to help you and happy to answer any questions! Email: email@example.com