Joomla / K2 / Simple image gallery pro

We have one project in Joomla K2 with Simple image gallery pro. The client needs a modification where the gallery can upload for example 10 images into simple image gallery pro but they want to select the images that can be visible in the gallery. Not delete but that exists just selection "Show in the gallery" because a client wants to add some into the text and they don't want to duplicate the images over and over again.
We have a full explanation.