Attach and Unattach is a very simple plugin which allows attaching and detaching images and other media to/from WordPress posts,
pages and other content types.
In the current WordPress versions, the only way to attach a media item to a post is if it wasn't attached before. The only
way to unattach is to remove the media item completely and upload it again (or to delete the post).
This plugin solves that adding a 'Attach' and a 'Unattach' link below each media file in the Media Library admin view.
Plugin by WePoSolutions