copy asset library contents

There is no built-in feature to do what you want.

SS is not suitable to store master versions of your images. SS does heavy processing when you upload images which alters them.

If you want pure versions of your images. Your hard drive or some other file storage service is much more appropriate.

There aren't any fancy high-end user interface bits of code to bulk download images but it might be possible to use a tool like wget or cURL to get images from your site. If you are not familiar with those tools then you'd need to work with a consultant to see if what you want can be done.