diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-includes/js/tinymce/plugins/wpgallery/plugin.js
--- a/wp/wp-includes/js/tinymce/plugins/wpgallery/plugin.js	Tue Jun 09 11:14:17 2015 +0000
+++ b/wp/wp-includes/js/tinymce/plugins/wpgallery/plugin.js	Mon Oct 14 17:39:30 2019 +0200
@@ -10,7 +10,7 @@
 	function html( cls, data ) {
 		data = window.encodeURIComponent( data );
 		return '<img src="' + tinymce.Env.transparentSrc + '" class="wp-media mceItem ' + cls + '" ' +
-			'data-wp-media="' + data + '" data-mce-resize="false" data-mce-placeholder="1" />';
+			'data-wp-media="' + data + '" data-mce-resize="false" data-mce-placeholder="1" alt="" />';
 	}
 
 	function restoreMediaShortcodes( content ) {