plugin.js

(function ($, Drupal, CKEDITOR) {
  var myPluginSaveCallback = function(data) {
    var content = data.image_render;
    insertContent(content);
  };
  CKEDITOR.plugins.add('myplugin', {
  	icons: 'imagepopup',
      hidpi: true,
      beforeInit: function (editor) {
  		// Implementation before initializing plugin.
  		editor.addCommand( 'editmyplugin', {
        canUndo: true,
        exec: function (editor, data) {
          // Populate existing values of form.
          var existingValues = {};
          // Open dialog form.
          Drupal.ckeditor.openDialog(editor,
            Drupal.url('my_module/dialog/image/' + editor.config.drupal.format),
            existingValues,
            myPluginSaveCallback,
            {}
          );
        }
      });

      editor.ui.addButton('MyPlugin', {
        label: Drupal.t('My plugin'),
        // Note that we use the original image2 command!
        command: 'editmyplugin'
      });

      insertContent = function(html) {
        editor.insertHtml(html);
      }
    },
  });
})(jQuery, Drupal, CKEDITOR);