So, a little bit of a correction.
You need to modify this file:
/lib/editor/atto/plugins/image/yui/build/moodle-atto_image-button/moodle-atto_image-button.js
Then use a js minimizer (there are tons of sites on the net) and then replace the code in
/lib/editor/atto/plugins/image/yui/build/moodle-atto_image-button/moodle-atto_image-button-min.js
Do a PURGE CACHE, and it works fine.