This plugin automatically uploads images dropped into Atto (from your computer) as though you'd stepped through the process of inserting an image, choosing to upload a new file.
Note that this only works in browsers which support dropping files into the page - IE10+, Firefox, Chrome, Safari and Opera. Other (or older) browsers will typically attempt to open the dropped file instead.
This plugin is for Moodle 2.7 and 2.8 only, as the functionality it provides has been incorporated into Atto's standard "image" plugin from Moodle 2.9 onwards.
This plugin does not add a toolbar button or any other visible UI to Atto - it simply detects images dragged and dropped into Atto, automatically uploading them to Moodle. It does still need to be in your Atto toolbar configuration in order to work, though in most cases this should happen automatically as part of the installation process.