[MAC][iMessages] How to delete selected photos in detail view of iMesssages

I am trying to delete multiple photos in the detail view (not sure how to call this view, it's the "!" icon at right top iMessages window)

I do believe it's allow us to do multiple photo selection. but just won't know how to delete those photos i selected.

Does anyone suffer this? I used to delete photo in this detail view since it's allow you view all photos in one place.