--- a/wp/wp-content/themes/twentytwelve/content.php	Mon Jun 08 16:11:51 2015 +0000
+++ b/wp/wp-content/themes/twentytwelve/content.php	Tue Jun 09 03:35:32 2015 +0200
@@ -17,7 +17,10 @@
 		</div>
 		<?php endif; ?>
 		<header class="entry-header">
-			<?php the_post_thumbnail(); ?>
+			<?php if ( ! post_password_required() && ! is_attachment() ) :
+				the_post_thumbnail();
+			endif; ?>
+
 			<?php if ( is_single() ) : ?>
 			<h1 class="entry-title"><?php the_title(); ?></h1>
 			<?php else : ?>