Yeah, and as is usually the case, it's not Preview in particular doing it. Preview itself does almost nothing, it's just a wrapper around the standard file hand

Yeah, and as is usually the case, it's not Preview in particular doing it. Preview itself does almost nothing, it's just a wrapper around the standard file handling libraries that everything on the platform uses. So this is just a normal thing you can do in nearly any context that any image is displayed anywhere on macos/ios. Not only no external site required, but not even any particular application required.