Most of the time, it will be able to deduplicate them. For example, if you save this page https://groups.google.com/a/chromium.org/g/chromium-extensio..., each different avatar will be embed only once. To achieve this, SingleFile stores the content of duplicate images in CSS custom properties, displays them as background images in the IMG tags and uses a (properly sized) transparent SVG image as SRC. Thus, stylesheets are not broken.
In fact, SingleFile implements several ways to save space. In practice, the most effective mechanism is shaking the CSS tree.
It's amazing how much CSS is useless in a page. It's especially annoying for SingleFile if it contains images... That's why SingleFile removes (almost) all unused rules, selectors and CSS properties by calculating the CSS cascade.
