General developer forum

I would guess that this is not possible unless get make a change to standard Moodle image icon - which would be a perfectly reasonable thing to do. Your use of a preview image in the editor, then replace it with a filter seems like a really nice idea.

What I would suggest is that you add a class like 'not-user-editable-image' to the IMG tag, then submit a change to core Moodle so that in lib/editor/atto/plugins/image/yui/src/button/js/button.js, the CSS selectors all have :not(.not-user-editable-image) added. Or something like that. (Probably not the best CSS class name to use. An alternative class name might beatto_image-ignore.