Shopify only allows us reaching images in the product media section, collection, asset and blog images.

Product media (or gallery) images can be found in your Shopify product section.

Main collection image is the image that you attach to the collection.

Featured blog image is the image that you attach to the blog post. We cannot reach images in the "Content" section as those are stored in Shopify files section.

Asset images are images that are added by a theme, depending on a theme these might be country flags for languages and currencies, magnifying glass icon for a search bar, etc. You can find it by navigating to Online store -> Themes -> Edit code

Images in the files section, 3rd party app images are not reachable to us sadly. For such images we have a manual optimization box in our dashboard.

To navigate to the manual optimization box, first you need to Optimize images section.

Then wait until your recent optimizations are loaded. After that scroll down and you'll see the manual optimization box.