When working in MultiStore mode, your various shops will be displayed in the Images panel (Properties column on the right handside) shown as columns with their names. This allows you to decide on the image(s) to share (make available) on your different shops, by simply ticking the corresponding boxes.
Note that when you share a product via the MultiStore Sharing Manager panel, then images associated to that product will be automatically shared on the same shops. This is an option enabled by default on the toolbar of the MultiStore Sharing Manager panel - slightly greyed out when enabled.
You can of course disable this option (click on it) if you want to decide which images to share on our shops, rather than having images shared automatically when you share the product.