Hi,
You can overwrite below file to restrict the images display on left rail (asset finder) of page based on path, naming convention, user permission etc, so that author wont be able to drag and drop in components as images wont be visible on asset finder.
/libs/cq/gui/components/authoring/assetfinder/asset/asset.jsp
(The path is from AEM 6.4 and might be same or different in other versions of AEM)
Hope this helps..